How to read a cordless tool spec sheet: volts, Ah, torque, RPM, IPM and UWO

The figures at a glance

Voltage: a label, not a contest

DEWALT's own footnote explains that 20V MAX is the battery's maximum initial voltage measured without a workload, and that the nominal voltage is 18. Milwaukee's M18 and CRAFTSMAN's V20 sit in the same class. So a "20V" tool and an "18V" tool are the same class of battery described two ways. The meaningful voltage difference is between classes: 12-volt-class lines (DEWALT 12V MAX, Milwaukee M12) and 18-to-20-volt-class lines. More on DEWALT's labels in FLEXVOLT batteries explained.

Amp-hours: runtime, size and weight

Ah is how much charge a battery holds. Within one voltage class, a 4 Ah pack runs about twice as long per charge as a 2 Ah pack on the same tool and job, and it is larger and heavier. Across classes, Ah is not comparable on its own: energy is voltage times amp-hours, so 2 Ah at 12-volt class holds less than 2 Ah at 18-volt class. Milwaukee groups its packs by size as well: CP (most compact and lightest), XC (balance of size and runtime) and HD (largest, longest runtime), per its battery FAQ.

Torque: convert, then compare kinds

Torque is the turning force. Makers state it in inch-pounds (in-lb), foot-pounds (ft-lb) or newton-metres (Nm): 12 in-lb is 1 ft-lb, and 1 Nm is about 0.74 ft-lb. Convert to one unit before comparing; our torque units guide has the conversions and a worked case. Then make sure you compare the same kind: tightening (maximum) torque and breakaway (nut-removal) torque are different measurements and are not comparable with each other.

RPM and IPM: speed and blows

RPM is the top speed of the spindle with no load; on a drill with two speeds, makers give both, such as DEWALT's 0-450 and 0-1,500 RPM for the DCD771. A higher top speed drives small screws and drills small holes faster; the low range gives more control and more turning force for large bits.

IPM (impacts per minute), which CRAFTSMAN calls BPM (blows per minute), is only on impact tools. It is how many hammer blows the mechanism delivers each minute at top speed. Milwaukee states 0-3,400 RPM and 0-4,200 IPM for the 2850 impact driver. The two figures belong together: the bit turns at the RPM, and the hammer strikes at the IPM when the screw resists.

UWO: DEWALT's own power measure

DEWALT rates many drills in unit watts out, such as 300 UWO for the DCD771. It is a measure of power, not torque, and other makers do not publish it. There is no conversion from UWO to in-lb, so a DEWALT drill rated in UWO and a Milwaukee drill rated in in-lb cannot be ranked from their spec sheets. Compare DEWALT drills with each other by UWO, and compare across makers on speed, chuck size and the jobs you have. See DEWALT 20V MAX vs Milwaukee M18 for a worked example.

Brushless

A brushless motor is a feature the maker names when it is there. We report it only where the maker or listing names it; its absence from a listing is not proof the motor has brushes.

A five-step check for any two tools

1. Same voltage class? If not, compare the system, not the tool.
2. Torque in the same unit and of the same kind? Convert, and set breakaway figures aside.
3. Speeds at the same setting? Compare top speed with top speed.
4. Kit or tool only? A "tool only" listing has no battery or charger; see combo kits compared.
5. Any figure only one maker uses (such as UWO)? Use it within that maker's range only.

What this page does not tell you

We do not test tools and we do not rank them. Figures change between model versions; the maker's page for your exact model number is the authority.