How to Choose the Right Torque Range: Understand Nm, ft-lb, and in-lb in One Minute
How to Choose the Right Torque Range: Understand Nm, ft-lb, and in-lb in One Minute
When buying a torque wrench, one of the most confusing things for beginners is torque units — Nm, ft-lb, and in-lb. They all measure the same thing (torque), but in different systems. Understanding them will help you choose the right wrench and avoid over-tightening or under-tightening bolts.
1. What Is Torque?
Torque is the rotational force applied to a fastener (like a bolt or nut).
In simple terms:
Torque = Force × Distance
If you tighten a bolt with a long handle, you apply more torque with the same force. That’s why torque wrenches are so useful — they ensure you apply the correct amount of torque every time.
2. Common Torque Units Explained
|
Unit |
Full Name |
Common Use |
Conversion |
|
Nm |
Newton Meter |
Widely used in Europe and Asia |
1 Nm = 0.738 ft-lb |
|
ft-lb |
Foot-Pound |
Common in the U.S. automotive industry |
1 ft-lb = 1.356 Nm |
|
in-lb |
Inch-Pound |
Used for smaller applications (like bikes or electronics) |
1 ft-lb = 12 in-lb |
💡 Tip: Don’t confuse ft-lb (foot-pound) with lb-ft (pound-foot). They mean the same thing — just a matter of format.
3. Which Torque Range Do You Need?
Here’s a quick guide for typical applications:
|
Application |
Recommended Range |
Common Drive Size |
|
Electronics / Small Devices |
10–200 in-lb (≈1–20 Nm) |
1/4" drive |
|
Bicycles / Motorcycles |
2–60 Nm (≈20–530 in-lb) |
1/4" or 3/8" drive |
|
Cars / Auto Repairs |
20–200 Nm (≈15–150 ft-lb) |
3/8" or 1/2" drive |
|
Heavy Machinery / Trucks |
200–1000 Nm (≈150–750 ft-lb) |
1/2" or 3/4" drive |
If your work often falls between two ranges, it’s better to choose the wrench that covers your most frequent torque needs rather than the highest possible value.
4. Quick Conversion Formula
If your manual lists torque in a different unit, use this:
- Nm × 0.738 = ft-lb
- ft-lb × 1.356 = Nm
- in-lb ÷ 12 = ft-lb
Or, simply use a digital torque wrench that can switch units with one button — it saves time and prevents mistakes.
Final Thoughts
The right torque wrench isn’t just about accuracy — it’s about matching the right range and unit to your work.
Whether you’re tightening a bike stem, changing spark plugs, or assembling machinery, understanding these three units (Nm, ft-lb, and in-lb) will help you pick the perfect tool for the job.