Foot Pounds to NM Calculator & Torque Conversion

This calculator converts torque from foot-pounds (ft-lb) to newton-meters (Nm) and back. Enter a value in either unit, and you get the equivalent in the other unit instantly. It uses the standard conversion factor: 1 foot-pound = 1.3558179483 newton-meters.

Formula

The conversion is a simple multiplication: Nm = ft-lb × 1.3558179483. The number 1.3558179483 is the exact conversion factor between the two torque units. It comes from the definitions of the pound (0.45359237 kg) and the foot (0.3048 m), combined with standard gravity (9.80665 m/s²).

To go the other way: ft-lb = Nm ÷ 1.3558179483.

Variables:

• Nm – torque in newton-meters (SI unit)
• ft-lb – torque in foot-pounds (imperial/US unit)
• 1.3558179483 – conversion factor (dimensionless)

Worked Example

Using the default value of 100 ft-lb:

1. Start with the formula: Nm = ft-lb × 1.3558179483
2. Plug in 100 ft-lb: Nm = 100 × 1.3558179483
3. Multiply: Nm = 135.58179483
4. Round to two decimals: 135.58 Nm

The calculator shows 135.58 Nm for 100 ft-lb, exactly matching this result.

What Are Foot-Pounds and Newton-Meters?

Torque is a twisting or rotational force. It measures how much force acts at a distance from a pivot point. Foot-pounds and newton-meters are two different units for the same physical quantity.

A foot-pound is the torque produced by a force of one pound acting at a perpendicular distance of one foot from the pivot. A newton-meter is the torque produced by a force of one newton acting at a perpendicular distance of one meter. The newton is the SI unit of force, defined as the force needed to accelerate one kilogram at one meter per second squared.

The imperial system uses foot-pounds for torque in the US, while most of the world uses newton-meters. You’ll see both on car specs, bicycle components, and industrial equipment.

Why the Conversion Factor Is Not Round

Many people expect 1 ft-lb to equal exactly 1.35 Nm or 1.36 Nm, but the true factor is 1.3558179483. The odd number comes from the definitions of the pound and foot relative to SI units.

The pound is defined as exactly 0.45359237 kilograms. The foot is exactly 0.3048 meters. Standard gravity is 9.80665 m/s². When you multiply these together (0.45359237 × 0.3048 × 9.80665), you get 1.3558179483. This is not an approximation; it’s the exact defined relationship.

Using a rounded factor like 1.36 introduces an error of about 0.3%. For most casual work that’s fine, but for precise engineering or when torquing critical fasteners, use the full factor.

Common Mistakes and How to Avoid Them

• Mixing up ft-lb and in-lb: Inch-pounds are 1/12 of foot-pounds. If you enter inch-pounds into a foot-pound converter, your result will be off by a factor of 12.
• Using the wrong direction: Dividing when you should multiply (or vice versa) gives an answer that’s off by the factor squared (about 1.84). Always check: 1 ft-lb is about 1.36 Nm, so Nm numbers are always larger than ft-lb numbers for the same torque.
• Rounding too early: If you round the conversion factor to 1.36 before multiplying, you lose precision. Do the full multiplication, then round the final answer.
• Assuming Nm and Joules are the same: They have the same dimensions (force × distance) but measure different things. Torque is a rotational quantity; work/energy is a linear quantity. Never compare them directly.

When to Use This Conversion

You need this conversion whenever you’re working with torque specs from different sources. For example:

• Your car’s service manual lists lug nut torque in ft-lb, but your torque wrench reads in Nm (or vice versa).
• You’re assembling a bicycle and the manufacturer specifies torque in Nm, but your tools are marked in ft-lb.
• You’re comparing torque specs between a US-made engine and a European engine.
• You’re reading an engineering document that uses one unit and need to apply it with a tool calibrated in the other.

Always use the same unit system that the original specification uses. Don’t convert unless you have to, because conversion introduces rounding errors. If you must convert, use the full factor and round only at the final step.

How to Read the Result

The result tells you the equivalent torque in the other unit. For example, if a bolt spec says 100 ft-lb, the calculator shows 135.58 Nm. If you set your torque wrench to 135.6 Nm, you’ll apply the same torque as 100 ft-lb.

For practical purposes, most torque wrenches have a tolerance of ±3-5%, so rounding to two decimals is plenty. If you’re doing precision work like engine assembly, use a calibrated wrench and follow the exact spec in its original units.

Remember that torque is a vector quantity – it has a direction (clockwise or counterclockwise). The conversion doesn’t change direction, only the numerical value.

Limits of the Conversion

The conversion factor is exact, so the formula itself has no error. The only limits come from how you use it:

• Input precision: If you enter a rounded value (like 100 ft-lb when the true spec is 100.5 ft-lb), the output will reflect that rounding.
• Display rounding: The calculator shows two decimals, which is more than enough for any real-world torque application.
• Unit ambiguity: Some older documents use “ft-lb” but mean “ft-lbf” (foot-pound-force) – that’s the same thing. But beware of “lbf-ft” which is also the same. The only real confusion is with inch-pounds.

If you need to convert between other torque units (like inch-pounds, kilogram-force meters, or dyne-centimeters), you’ll need additional conversion factors. This calculator handles the two most common units.

Frequently Asked Questions

How many Nm is 1 ft-lb?

Exactly 1.3558179483 Nm. For quick mental math, you can use 1.36 Nm, but for precise work use the full factor. The calculator uses the exact value.

How do I convert Nm to ft-lb without a calculator?

Divide the Nm value by 1.3558. For example, 100 Nm ÷ 1.3558 = 73.76 ft-lb. A rough estimate is to divide by 1.36, which gives 73.5 ft-lb – close enough for most casual use.

Is ft-lb the same as lb-ft?

Yes, they are the same thing. Foot-pound and pound-foot are both used, though “foot-pound” is more common in the US. The multiplication is commutative, so the order doesn’t matter. Both mean the same torque.

Why do car specs use Nm in Europe but ft-lb in the US?

It’s a matter of measurement systems. Europe (and most of the world) uses the metric system, where the SI unit for torque is the newton-meter. The US still uses imperial units, where foot-pounds are standard. Most modern car manuals include both to serve international markets.

Can I use this conversion for energy or work?

No. Although Nm and joules are dimensionally equivalent, torque is not energy. Torque is a rotational force, while work/energy is a scalar quantity. You cannot convert between torque and energy without additional information about rotation angle.

What if my torque wrench reads in kg-m or in-lb?

This calculator only handles ft-lb and Nm. For kg-m (kilogram-force meters), multiply Nm by 0.10197 to get kg-m. For in-lb, multiply ft-lb by 12 to get in-lb. You can do those conversions separately, then use this calculator for the main conversion.

Related

• Equivalent Length Calculator for Pipe Fittings
• Equal Circular Spacing Calculator: Position Points Evenly
• Equal Hole Spacing Calculator & Formula

in ft_lb | Foot-pounds | ft-lb | 100 | 0
out nm | Newton-meters | Nm | ft_lb * 1.3558179483 | 2
out ft_lb_out | Foot-pounds (from Nm) | ft-lb | nm / 1.3558179483 | 2