Aren't N·m and J (joule) the same unit?

They have the same dimensions but different physical meanings. Torque is a vector (rotational force), energy is a scalar (work). SI uses only N·m for torque, not J.

What is the difference between ft·lbf and lbf·ft?

Officially, lbf·ft = torque, ft·lbf = energy. But in practice, both are often called "foot-pounds." SAE standards use lbf·ft for torque.

Torque Unit Conversion | Eng Unit Converter

Torque Conversion Guide

Torque is a rotational force that causes angular acceleration, calculated as force multiplied by the perpendicular distance from the pivot. The SI unit is newton-meter (N·m). Despite having the same dimensions as energy (joule), torque is a fundamentally different quantity. Key conversions: 1 N·m = 0.7376 lbf·ft, 1 lbf·ft = 1.3558 N·m, 1 kgf·m = 9.80665 N·m, 1 lbf·in = 0.1130 N·m. Power and torque relate via P = T × ω, or HP = T(lbf·ft) × RPM / 5252. Torque conversion is essential in automotive engineering (engine output, bolt tightening), mechanical assembly (fastener specifications), robotics (joint actuators), and rotating machinery design. Critical pitfalls: using joules for torque (incorrect by convention even though dimensions match), confusing lbf·ft (torque) with ft·lbf (energy) in US practice, and neglecting to convert between N·m and kgf·cm when working with Asian-manufactured motors and actuators that often use kgf·cm in specifications.

! Torque — Good to Know

N·m (torque) and J (energy) have the same dimensions but are different physical quantities. Never use "joules" for torque.
Convention: torque is "force×distance" (lbf·ft, N·m), energy is "distance×force" (ft·lbf). In practice, they're often mixed.

Torque

Torque Conversion Guide

! Torque — Good to Know

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