Understanding Torque Specs: What the Numbers on Your Tools Mean
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Every drill, impact driver, and wrench has a torque number on the spec sheet. That number gets compared, debated, and misunderstood. A 2,000 in-lb impact driver doesn't deliver 2,000 in-lbs to the fastener. A 300 ft-lb impact wrench doesn't apply exactly 300 ft-lbs to a lug nut. The numbers on the box are measured under specific test conditions that don't match your job site. This guide explains what the numbers actually represent, how to compare them across tools, and when the number on the box matters less than you think.
Inch-Pounds, Foot-Pounds, and Newton-Meters
Three units measure the same thing: rotational force. Inch-pounds (in-lbs) are used for drills and impact drivers. Foot-pounds (ft-lbs) are used for impact wrenches and automotive torque specs. Newton-meters (Nm) are the metric equivalent, common on European and Asian tools and in automotive service manuals.
The conversions: 12 in-lbs equals 1 ft-lb. 1 ft-lb equals 1.36 Nm. A drill rated at 1,200 in-lbs delivers 100 ft-lbs or about 136 Nm. An impact wrench rated at 300 ft-lbs delivers 3,600 in-lbs or about 407 Nm. Keep a conversion chart in your toolbox or your phone if you switch between US and metric specs.
How Torque Is Measured
Manufacturers test torque at the chuck or output shaft with no bit, no fastener, and no workpiece. The tool drives against a calibrated sensor that measures the peak force. The number you see is the maximum the tool produced under those ideal conditions. Your real-world torque is always lower because the bit, fastener, and material all absorb energy.
Impact tools are especially tricky. An impact driver doesn't deliver a constant 2,000 in-lbs. It delivers rapid bursts that peak at that number. The effective torque at the fastener depends on the fastener's friction, the material, and how many impacts it takes to seat. A 2,000 in-lb impact driver and a 1,800 in-lb impact driver feel nearly identical driving deck screws because the real-world torque delivery depends on so many variables beyond the motor's peak output.
Breakaway vs. Sustained Torque
Impact wrenches list two torque numbers. Breakaway torque (also called nut-busting torque) is the peak burst the tool delivers to crack a stuck fastener loose. Sustained torque (also called running torque or fastening torque) is the continuous output during driving. Breakaway is always 20% to 50% higher than sustained.
When a manufacturer puts one big number on the box, it's usually breakaway. That's the impressive number. Check the spec sheet for both values. A wrench with 700 ft-lbs breakaway and 500 ft-lbs sustained tells you more than a headline "700 ft-lbs" alone. If a lug nut is rusted to 600 ft-lbs, the 700 ft-lb breakaway might crack it. The 500 ft-lb sustained number wouldn't.
Matching Torque to the Task
More torque doesn't automatically help. Driving drywall screws into studs needs about 25 in-lbs. A 2,000 in-lb impact driver snaps the screw head off if you pull the trigger all the way. That's why speed control modes exist. DeWalt, Milwaukee, and Makita all offer 3 to 4 speed settings on their impact drivers so you can match the output to the fastener.
For drills, 400 to 700 in-lbs handles 90% of homeowner tasks: pilot holes, cabinet screws, shelf brackets. 1,000 to 1,500 in-lbs is the pro range for driving lag screws and boring large holes. Above 1,500 in-lbs, you're in specialty territory: structural fastening, heavy timber, and engineered connections. If you're not doing that work, the extra torque is wasted money.
Why Spec Sheet Comparisons Aren't Enough
Torque numbers tell you about the motor's capability. They don't tell you about control, ergonomics, speed settings, trigger response, or how the tool feels in your hand. A 1,500 in-lb driver with 4 speed modes and a responsive trigger is more useful on a varied job than a 2,000 in-lb driver with one speed and a binary trigger. Read reviews, borrow a tool from a friend, or try it in the store before buying based on numbers alone.
Frequently Asked Questions
What torque do I need to remove lug nuts?
Lug nuts are typically torqued to 80 to 100 ft-lbs on passenger cars and 100 to 150 ft-lbs on trucks. Rusted or overtorqued lugs can seize at 150 to 200+ ft-lbs. An impact wrench with 250+ ft-lbs of breakaway torque handles most passenger vehicles. For trucks and seized fasteners, 500+ ft-lbs is safer.
Do I need a torque wrench if I have an impact wrench?
Yes. An impact wrench removes fasteners and runs them down to approximate tightness. A torque wrench sets the final torque to the manufacturer's specification. Impact first (fast), torque wrench second (precise). They're complementary tools.
Can too much torque damage a fastener?
Absolutely. Over-torque stretches the bolt, strips the threads, cracks the casting, or snaps the head off. On automotive engines, where torque specs are calibrated to specific clamping forces, over-torque can warp components and cause leaks. Follow the spec.
Why do some tools list torque in Nm instead of ft-lbs?
The tool was designed or marketed for regions that use metric units. Most tool specs list both, but some import tools only show Nm. Multiply Nm by 0.74 to get ft-lbs. Or multiply ft-lbs by 1.36 to get Nm.