When shopping for power tools, most professionals want the same thing–reliable power at the best price. The prices are always clear enough, but how do you compare performance without dragging the tools onto the jobsite first?

"Everyone looks at the same things–amps, rpm, horsepower, torque–and thinks more is better," says Dwight Sherman, president of Berland's House of Tools, a Chicago-area tool retailer catering to the professional user. "But that's not necessarily true."

"Amps and horsepower are misleading," agrees Chris Webber, vice president of merchandising for Lowe's. "Unfortunately, the industry has trained both pros and DIYers to think that amps and horsepower are meaningful ratings."

"It's Mom, apple pie, and bigger is better," says Doug Bock, national sales manager of Panasonic's power tool division, describing the tenor of the U.S. tool market. "The problem is manufacturers don't measure the numbers in the same way, and sometimes what they measure has nothing to do with power."

When asked about the numbers they report, representatives for nearly every manufacturer of professional-grade power tools agreed there is seldom a relation between one manufacturer's numbers and another's, rendering the specifications virtually useless as a basis for comparison. The one exception may be a corded power tool's amp rating, which is tested to Underwriters Laboratories standards. This UL listing is an electrical safety standard required for all products powered by electric motors, but it has nothing to do with power output.

Rating the Ratings

To understand these issues, let's first run down exactly what the numbers mean, focusing on the common power ratings for electric motors: Amps. A tool's amp rating indicates the electrical current load the motor can carry for an indefinite period of time without degrading the insulation and other electrical components. In a UL-rated tool, the motor is tested to verify that it operates at or below a specific temperature when current flows through it. Heat is the chief variable the test measures, so a tool's amp rating depends on the amount of heat absorbed and dissipated by the motor's "active materials" (windings, laminations, and other conductors). An amp rating also depends on motor speed (measured in rpm), since the faster the motor, the better it can draw air through the tool to carry away heat. Strictly speaking, an amp rating indicates the maximum allowable continuous current a motor can handle without exceeding temperature limits. In other words, a tool's amp rating measures how effectively a motor cools itself, not how powerful it is.

The current that a motor can sustain continuously without burning out its windings is a fraction of the current at maximum load. Plunge an underpowered saw into a long rip of wet pressure-treated lumber and it will draw much more current than its amp rating. The motor will heat up more than it should, too, and the insulation will begin to break down. Do this too much and the motor will burn out in a relatively short time. Or, the more immediate result: If you push a low-powered tool too hard, it will draw more current than the circuit allows and pop the breaker. The association between power and amps stems from such effects, but the actual power output depends on so much more than current draw.

"The assumption has always been that the more energy going in, the more energy can come out," explains Skip Nichols, technical manager for DeWalt Power Tools. "But that's not a fair assumption to make. The useable power coming out of a tool depends on the efficiency of the motor, as well as the gearing." So for example, a top-handle circular saw and a wormdrive saw may have the same amp rating, but because of two very different gearing systems, the two saws deliver different amounts of torque.

Dan Lewis, a product design manager at Makita, underscores the effect of motor efficiency on electric motor power. An efficient electric motor converts more of the electricity it draws into power and less into heat. "If the motor efficiency is high," Lewis argues, "you get more power with fewer amps required. That is why using the UL amp rating to judge a tool's power is absurd."

"There's plenty of black magic in the way toolmakers typically report horsepower," concurs Bryan Whiffen, senior vice president for product development for Ridgid Tool Co. "But the most black magic of all is in torque ratings, particularly for cordless tools."

Torque is a measure of rotational force, and on the face of it, seems to correspond to what most people mean by tool power–the strength to keep a saw blade or large-diameter drill bit spinning fast enough to cut efficiently, even in tough materials. To achieve real-world results, the torque output of a tool's motor shaft must be mechanically increased by the gears in the drive train, leading to higher torque at a saw's arbor or a drill's chuck. That torque, divided by the radius of the saw blade or the drill bit, equals the actual force that allows the blade or the bit to do its work.

But high torque can be misleading. For any tool, there is no single measure of torque. Rather, there is a range of torque measurements corresponding to the speeds at which a tool operates–from the fastest no-load speed to a complete stall (see graph, below). Torque is always related to the speed of rotation. The torque of a universal motor goes up as a load is applied and the speed of rotation slows down. The more you load a motor, the slower it runs until it stalls, at which point the torque is at a maximum.

According to Mickey Workman, a lead test engineer for Intertek Testing Services, the modern incarnation of Thomas Edison's original electrical testing lab, the best way to measure torque is by applying resistance to the rotating shaft and measuring the response while the motor is running. This way, torque can be measured within the range of operating speeds in which current flow is at or below the tool's UL-listed amp rating. This sustained torque reading would correspond to the actual power of the tool under normal operating conditions.

However, when most toolmakers publish a torque rating (which is now common for cordless drills), it's nearly always the stall torque, also known as breakdown torque–the highest reading possible. At the stall point, a tool is drawing the maximum current, and is generating the most heat. In short, stall torque reflects the very worst possible condition for operating a tool.

Horsepower is a mathematical expression of the relation between speed and torque. Depending on the torque figure that goes into the equation (either sustained or stall torque), horsepower can be reported as either a continuous running or peak rating. Most manufacturers of portable power tools list peak power–the highest number–but the same fallacy applies: If a motor were continuously operated at the load required to measure maximum output, the tool would quickly burn out because of the high current being pulled through the motor. Manufacturers justify this number by claiming it shows the power available to the tool to power it through a knot, or another short-lived, high-demand application. But in truth, if the horsepower rating depends on stall torque, a tool is unlikely to ever exhibit maximum power before it trips a breaker. It's simply not a realistic number.

Watts Out. A few manufacturers–most notably DeWalt and Makita–report watts out as a measure of motor power. Watts out is derived from horsepower by multiplying peak horsepower by 746 (1 hp = 746 watts). As a result, watts out numbers are higher than horsepower figures (for example, a 3-hp electric motor–measured at peak power–delivers about 2,220 watts out), but it's no more reliable as an indicator of sustained power than peak horsepower or stall torque.

Pneumatic Power

While only a few manufacturers give power ratings for pneumatic nailers, those published power specifications are troublesome. Nailers need enough power to sink a nail in stubborn materials, such as frozen wood or engineered lumber, without a carpenter having to finish them with a hammer. Finish nailers must have the power to set a nail in maple stair treads, for example. However, there is no reliable measure of the force with which a tool's driver blade buries a nail.

Driving Force. A couple of toolmakers–notably Senco and DeWalt–report the "power" or "energy" of a nailer's driving force by measuring the velocity at which a nail travels through a light beam. The test measures the fraction of a second it takes a nail to travel through the beam, which is then translated into inch-pounds of force by a complex formula. Stanley-Bostitch does a similar test, but buries the inch-pounds of force in a "power-to-weight ratio," arguing that the best tool in its class has the best balance of both variables. The rationale here is that it's easy enough to build a beast of a nailer capable of driving, say, 20d spikes through ironwood, but a carpenter might not be able to lift such a tool. Including weight in the equation is also a nod to the fact that power may not be the most important feature of a pneumatic nailer, but it doesn't cover up the fact that as a power rating, all of these numbers lack credibility.

When asked for comment on the practice of deriving force from velocity, John Kurtz, executive director of the International Staple, Nail and Tool Association (ISANTA), and an engineer by training, expressed his reservations about such a calculation. Measuring the speed of a nail through light cannot account for the resistance of the material into which the fastener would actually be driven. The reason for evaluating driving strength is to ensure a tool has the power to sink a nail in dense materials, Kurtz reasons. Any calculation would have to make assumptions about the difference between air and, say, Southern yellow pine–assumptions that Kurtz suggests would be questionable, at best. Pneumatic power depends on several variables–such as air pressure, the size of the hose, the size of the cavities within the tool, the displacement of the piston, and the distance it travels. "Many factors go into what we know of as power," says Kurtz, "but the speed of the nail through air is not one of them."

Durability. Ultimately, the force with which a driver blade punches a nail may not be the single most important feature for a nailer, particularly if a tool has an adjustable depth-of-drive. Intertek Testing Services' Workman reports that the durability and sustained performance of a nailer is typically what his lab is hired to evaluate. All of Intertek's nailer testing involves user trials–essentially turning someone loose with the nailers, firing hundreds of rounds into uniform substrates and keeping track of misfires, jams, and timing cycle rates, and extrapolating the results. "The goal is to come up with a picture of the tool's performance. Manual testing can often give you a more realistic picture than a machine can," says Workman. While every effort is made to keep variables consistent and the test reliable, the picture contained in Intertek's evaluation report is hardly a concise number that would fit neatly in a specifications list. It's conceivable to Workman that a standard rating could be derived, but it could only be significant if the entire industry adopted the procedure and agreed on a rating scale.

Cycle Rate. Paslode specifies cycle rate in terms of nails per second that a tool can fire, which is arguably an important indicator of how fast a tool will recover when bounce-nailing. The faster the cycle, the faster a carpenter can move without the nails stair-stepping. While this number may reflect a certain efficiency afforded by a tool, it's not widely reported. Several toolmakers expressed their reluctance to report cycle rates without tying it to air temperature, which can dramatically affect the behavior of O-rings and other moving parts in a pneumatic tool. "If you say a tool performs one way, someone in Iceland will sue you for making a false claim," says Chris Dutra, director of product management for Stanley Fastening Systems.

Alleged Distortions

Dutra is not the only one to express a wariness of litigation. A recent class-action lawsuit has forced compressor manufacturers to stop advertising inflated values for compressor horsepower. The lawsuit alleged that the companies "labeled, promoted, and sold consumer air compressors with electric motors as having higher horsepower motors than they in fact contained." The defendants, including Campbell Hausfeld, Coleman Powermate, DeVilbiss, and Ingersoll-Rand Co., ultimately settled the suit, agreeing to compensate buyers of the questionable compressors with up to $50, potentially amounting to millions in compensation from each defendant named in the suit. In addition, the companies agreed to stop labeling 110-volt electric-powered air compressors with peak horsepower or related terms, such as "peak power," "max developed power," "max kinetic power," or "breakdown torque." Despite agreeing to the settlement, the defendants deny the allegations, deny liability, and deny that any plaintiff in the suit is entitled to relief of any kind.

One power-tool marketing manager who spoke only on condition of anonymity claims this lawsuit reached far beyond compressor manufacturers, changing the entire tool industry overnight. "We immediately had to remove all horsepower statements from every tool–not only our compressors, but also routers, saws, any tool indicating horsepower. Every mention was removed or changed to specify 'peak horsepower,' not just 'horsepower.' We changed everything–the tool, the box, the catalog. If we didn't, we would have been sitting ducks for any lawyer out there."

The compressor settlement harkens back to lawsuits brought against stereo equipment manufacturers for exaggerated power ratings for speakers and speaker output, which eventually prompted the Federal Trade Commission to set standards for reporting power specs in terms of "continuous average power." Under FTC guidelines, audio power specs, such as speaker wattage, must always be accompanied by statements of impedance, distortion, and bandwidth, variables that have an impact on sound quality. Without a clear specification of these numbers, consumers would have no way of understanding the quality of the sound output, which could be extremely poor at higher wattage levels. In the end, litigation may be the impetus for an organization such as the Power Tool Institute (PTI) to initiate voluntary performance standards. PTI failed to respond to our queries about performance standards, but several member-representatives of power tool manufacturers in the organization admitted that there have been ongoing committee discussions to address the topic of performance standards.

"PTI's reason for being is to keep the Consumer Products Safety Commission out of the industry," one member-representative said. "If more class-action suits arise, there will be much more pressure brought to bear on quality standards. It would change the face of PTI considerably."

PTI, which claims on its Web site to be "the preeminent organization for building global understanding of power tools and for maintaining high standards of safety and quality control in the industry," has mostly focused on the safety side of its mission statement. The organization offers several information products addressing the safe use of power tools. But with the exception of one Web page that addresses tool maintenance and a page about proper battery recycling, it offers no information to the public about tool performance, tool quality, or definitions of performance ratings.

When asked about performance standards,ISANTA executive director Kurtz said there were currently no discussions within his organization on the topic of rating tool performance, but plenty on fastener performance. "ISANTA has its hands full with technical standards relating to the strength of fasteners and tool safety standards. Keeping up with the building codes keeps us busy."Several ISANTA member representatives agreed that the primary focus of the organization was to sponsor evaluation reports, principally through the National Evaluation Service, to ensure that the fasteners used in the tools meet the requirements of the building codes.

Meaningful Standards

At this point it's unclear who will take responsibility for providing meaningful performance standards, but as the industry changes, the need among both tool buyers and tool makers for clear, comparative measures can only increase. Price pressure will continue to drive more and more professionals to big-box outlets, such as The Home Depot and Lowe's, and to Internet and mail-order channels where the published specifications list increasingly has become the principal basis for comparing one tool to another.

According to Randall Coe, director of product development for Bosch Power Tools, when there is no salesperson to weigh in on the spectrum of features and applications, much more importance falls on the point of purchase (POP) display. "On-shelf competition is heating up in a salesperson-free situation. POP specs become extremely important," he says.

Another tool-company representative, speaking about rules for promotions established in The Home Depot stores, comments, "Now we have to make our case with something like five bullet points on a standardized card." In such a marketing environment, the pressure increases to concisely define how one tool stands out from another.

"Every manufacturer wants to press its advantage," explains Coe. "Bosch likes to focus on innovative features. Generally, if all a company has to talk about is amps, that usually means there's nothing else to say."

Mike Farrah, global product merchant of power tools for The Home Depot, would like to see the criteria even more sharply defined. "It's time for the industry to get off the dime," Farrah urges, pointing out that when you dig beneath the surface to understand a number like amps or torque, the first thing that's evident is that every toolmaker measures and reports specifications differently. "Without standard test procedures, the numbers are meaningless," he says.

This lack of conformity may drive The Home Depot to institute its own version of standards, at least for professional-grade tools. Farrah suggests that as a fallback measure, The Home Depot has considered designating a leading manufacturer in each tool category to define standard testing procedures. The company would then require that every tool in the category sold in The Home Depot, (and presumably in its newly acquired White Cap Construction Supply stores, as well) be tested by that procedure.

The advantage to such a proposal is that everyone would test and report the numbers in the same way. However, the suggestion begs the question of how The Home Depot would treat its "house brand" of tools. "If Ridgid comes out ahead in even one category, it would be suspect," says one tool marketer. Perhaps it is this concern that prompted Farrah to qualify his suggestion as a "fallback" position. "Certainly we would prefer that an association such as the PTI develop standards," Farrah says.

Not Just Numbers

While there is a general consensus that some common performance rating would give tool buyers a fair basis for comparing tools, toolmakers are also quick to downplay a market based only on numerical standards. Boiling a comparison down to numbers overlooks the range of features that actually distinguish one tool from another. Particularly in professional-grade tools, where power ratings are roughly equivalent, power is seldom the defining feature.

"There's more than just numbers," claims Senco product manager Charlie Lytle. "The materials the tool is made from, the durability, how much abuse a tool can take, its balance–these are some of the things that ultimately make the most difference."

Bock contends that the numbers also can be deceiving. "I'd be surprised if anyone can really tell the difference between 440 and 500 inch-pounds of torque. But in a lineup of tools, the higher number is perceived as better."

Tool marketers frequently suggest that the prevailing mentality among tool buyers is that bigger is better. "It goes beyond power. It works with blade size, too," says Coe, citing the success of 12-inch miter saws as one example of a tool category that dominates the market, even though carpenters can often do a majority of the work with smaller, less expensive models.

In a further example of how the industry will continue to respond to big numbers, Coe predicts that there could be a gradual escalation in amp ratings for categories like jigsaws and other tools that have not reached the 15-amp ceiling, much like there has been with reciprocating saws in recent years. "Even if it doesn't make sense, in the absence of real innovations, marketers will be inclined to run that race," Coe concludes.

Clayton DeKorne reports on technology and training for the trades from home bases in Brooklyn, N.Y. and Burlington, Vt.