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Impact Drivers, Explained

After reading, you'll know why two drivers quoting the same torque may not be comparable, and which numbers to buy on instead.

Updated August 23, 2026 · Companion to our Tech & Gadgets review

DEWALT DCF850B ATOMIC 20V MAX 1/4 in. 3-Speed Brushless Impact Driver - our top pick
In this guide

Every impact driver is sold on inch-pounds. No standard says how that figure is produced, and it usually describes undoing a fastener rather than driving one.

The 30-second version

  • No standard governs impact torque, so set time, fastener size and rig are the manufacturer's own choices, and figures are not reliably comparable between brands.
  • The headline is usually breakaway torque, the force to loosen a seized fastener, while real fastening output tends to be roughly half to two thirds of it.
  • Head length decides more jobs than torque, because a driver that will not fit between joists or inside a cabinet cannot apply any of its output.
  • Impacts per minute drive the speed, since a long fastener goes in on the rate of hammer blows as much as on the force behind each one.
  • A low mode prevents the common failures, as bits walking at the start and screws burying in soft material cause more ruined work than insufficient torque does.

The products this guide is about

Our verdict on each, with the full reasoning on the companion review.

What actually matters

  • Torque in inch-pounds - the headline, produced by an unregulated in-house test. Use it to place a tool in a rough tier, not to make fine comparisons. Convert if needed: 1,000 in-lb is about 113 Nm.
  • Fastening versus breakaway - breakaway is loosening force and is the bigger figure. If a maker does not say which it is quoting, assume the flattering one.
  • Head length - front to back, the dimension that determines access in stud bays, cabinets and engine bays. Unambiguous and directly comparable, and frequently unpublished on budget tools.
  • Impacts per minute - the hammer blow rate. Together with RPM it sets how quickly a fastener actually seats, which torque alone does not describe.
  • Speed settings and assist modes - a dialled-down mode or a soft-start assist prevents cam-out and over-driving. More useful on trim and cabinetry than raw output.
  • Battery platform - a bare tool price is not the purchase price. The platform you join determines what every future tool and battery costs.

The specs, in plain English

Impact driverA driver that delivers rotational hammer blows as well as rotation, so the reaction force goes into the tool instead of your wrist. Takes 1/4 inch hex shank bits only.
Breakaway or nut-busting torqueThe force needed to loosen an already-tight fastener. Larger than fastening torque and commonly used as the headline figure.
Fastening torqueThe force the tool applies while driving a fastener in. The number that matters for most work, and rarely the one advertised.
IPMImpacts per minute, the rate of hammer blows. Higher rates seat long fasteners faster at a given torque.
Head lengthFront to back dimension of the tool. Decides access between joists, inside carcasses and in engine bays.
Assist modeA programmed start that runs slowly until the fastener bites, then ramps up. Prevents the bit walking and the screw head stripping.
Brushless motorA motor with no carbon brushes to wear out, giving longer life, better efficiency and more run time per charge. Now common at every price.
Bare toolSold without battery or charger, on the assumption you own the platform. The cheaper sticker hides the real cost of entry.
Cam-outThe bit slipping up and out of the screw recess under load, rounding the head. The main thing low-speed and assist modes exist to prevent.

Green flags vs red flags

Green flags

  • Head length is published as a number rather than described as compact.
  • The torque figure is explicitly labelled as fastening or as breakaway.
  • Impacts per minute are published alongside RPM.
  • Speed and impact figures are given for every mode, not just the maximum.
  • A warranty term is stated in years, with any service period spelled out.

Red flags

  • A torque figure leads with no indication of how or on what it was measured.
  • Compact is claimed but no head length appears anywhere.
  • Impacts per minute are missing while torque is prominent.
  • Marketing quotes nut-busting torque and then compares it against rivals' fastening figures.
  • The specification table is shorter than the feature list.

Who's who: the brands

  • DEWALT - The ATOMIC line competes on head length and compactness at mainstream prices, with strong warranty terms and moderate published detail.
  • Milwaukee - M18 FUEL leads on raw output and impact rate, and is the most forthcoming here on physical dimensions. Uses nut-busting figures in marketing.
  • Makita - Builds control features rather than headline torque, with multi-mode assist settings and per-mode figures published in full.
  • CRAFTSMAN - Budget brushless tools on the V20 platform. Adequate output, and the thinnest published specifications of the major brands.
  • Bosch - Strong in compact professional drivers, generally competing on ergonomics and control rather than on the largest torque number.

How to read a listing without getting fooled

Read the head length first, because it decides whether the tool can do the job at all, and treat its absence as a warning. Then check whether the torque figure is labelled fastening or breakaway, and if it is not, assume breakaway. Look for impacts per minute next to RPM. Only then compare torque numbers, and only as a rough tier, since no two makers measured them the same way.

How much should you spend?

Budget buys a brushless driver with enough torque for framing and assembly and very little published about it. Mid-range buys a compact head, multiple speed settings and a real warranty. Premium buys the highest output and impact rates, or the control modes that stop you ruining soft material, and you generally choose between those two rather than getting both.

Questions, answered

Can I use an impact driver to drill holes?

You can with impact-rated hex shank bits, and it will be worse than a drill. The hammering that makes an impact driver good at fasteners is unhelpful for cutting, producing rougher holes and more bit wear. It also takes only hex shanks, so ordinary round-shank drill bits will not fit at all.

Will more torque strip more screws?

Yes, if you drive everything at full speed. Stripping is usually a control problem rather than a power one, which is why assist modes and low speed settings exist. A high-torque tool with a usable low mode is safer on soft material than a low-torque tool with a single speed.

Why do impact drivers need special bits?

Because the hammer blows fatigue ordinary bits until they shatter. Impact-rated bits use a more ductile steel and often a torsion zone that flexes to absorb each blow. Using standard bits in an impact driver is the fastest way to snap one, and the pieces come out at speed.

Is 1,500 in-lb enough?

For deck screws, framing and flat-pack assembly, comfortably. The figures above 1,800 buy headroom for lag screws and seized fasteners rather than everyday capability. Given that none of these numbers was produced under a common standard, the gap between 1,500 and 1,825 is smaller in practice than it looks on paper.

Ready to choose? See our top pick, the alternatives, and the one we'd skip See the Impact Drivers verdicts

Or jump to the head-to-head: DEWALT DCF850B ATOMIC 20V MAX 1/4 in. 3-Speed Brushless Impact Driver vs Milwaukee 2953-20 M18 FUEL 1/4 in. Hex Impact Driver.

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