What is torque?
Torque is a measure of the rotational tendency that a force creates around an axis. When you use a wrench to tighten a bolt, you are applying a force at the end of the wrench handle. The torque you produce is not simply the force you apply — it depends on both the magnitude of that force and the distance from the pivot point (the bolt centre) to where you apply the force. Torque equals force multiplied by the perpendicular distance between the force and the axis of rotation.
In SI units, torque is measured in newton-metres (N·m). A torque of 1 N·m means you are applying a force of 1 newton at a perpendicular distance of 1 metre from the pivot. If you have a wrench that is 0.25 metres (25 cm) long and you apply 40 newtons of force at its end, you produce 10 N·m of torque. Doubling the wrench length to 0.5 metres with the same force produces 20 N·m. This is why breaker bars — long-handled wrenches — make it easier to loosen stubborn fasteners.
The Torque Converter supports 12 units across three families: SI prefixed units, Imperial force units, and metric-force units. Understanding the relationships between them helps you read specifications from any source correctly.
Torque versus work: same units, different physics
One of the most common sources of confusion about torque is that it has the same dimensional units as work and energy — force times distance. In SI terms, a joule (the unit of energy) is also a newton-metre. Yet torque and work are genuinely different physical quantities and should never be confused.
Work is a scalar quantity: it has magnitude but no direction. When a force moves an object through a distance in the direction of that force, work is done, and the energy transferred equals force times distance. A 10-newton force moving an object 1 metre in the direction of the force does 10 joules of work.
Torque is a vector quantity: it has both magnitude and direction (the axis around which the rotation occurs). A 10-newton force applied 1 metre from a pivot produces 10 N·m of torque in a specific rotational direction — but no work is done unless something actually rotates. The bolt being tightened does not care that the units look the same. The disambiguation matters in engineering calculations: when you see “N·m” in a rotational context, it means torque; when you see “J” or “N·m” in an energy context, it means work. Never add them together.
The 12 torque units and their conversion factors
The Torque Converter normalises all values through newton-metres as the internal reference unit. Here are the 12 supported units and their exact conversion factors.
The SI family covers six prefixed variants of the newton-metre. The base unit is the newton-metre (N·m). The kilonewton-metre (kN·m) equals 1,000 N·m and is used for large structural applications like bridges and industrial machinery. The decinewton-metre (dN·m) is 0.1 N·m. The centinewton-metre (cN·m) is 0.01 N·m. The millinewton-metre (mN·m) is 0.001 N·m and appears in specifications for small electric motors and precision instruments. The micronewton-metre (µN·m) is 0.000001 N·m and is used in MEMS sensors and laboratory measurements.
The Imperial family contains three units. The pound-force foot (lbf·ft) equals 1.35582 N·m and is the standard unit in American automotive engineering. The pound-force inch (lbf·in) equals 0.112985 N·m — useful for smaller fasteners where lbf·ft would produce fractional values. The ounce-force inch (ozf·in) equals 0.00706155 N·m and appears in specifications for small motors, servos, and electronics assembly.
The metric-force family uses the kilogram-force, which is the weight of a 1-kilogram mass under standard gravity (9.80665 m/s²). The kilogram-force metre (kgf·m) equals 9.80665 N·m and is common in older European and Soviet engineering documents. The kilogram-force centimetre (kgf·cm) equals 0.0980665 N·m. The gram-force centimetre (gf·cm) equals 0.0000980665 N·m and appears in specifications for hobby motors and micro-mechanisms.
Why European specs use N·m and American specs use lbf·ft
The divergence between N·m and lbf·ft reflects the broader split between the metric and Imperial measurement systems. The International System of Units (SI), which most of the world formally adopted in the second half of the twentieth century, designates the newton-metre as the standard unit for torque. European automotive manufacturers, following SI, express engine torque, fastener specifications, and service manual values in N·m.
The United States retained the Imperial system for most practical engineering and consumer applications. American automotive tradition uses pound-force feet for engine torque and service specifications. The SAE (Society of Automotive Engineers) publishes standards in both units but defaults to Imperial. This means that a mechanic trained in the United States needs to convert European specifications, and vice versa. A European car with a torque specification of 300 N·m at the engine shaft produces approximately 221 lbf·ft — a fact that matters when choosing a torque wrench with the right range.
Torque and horsepower: the relationship
In Imperial units, there is a precise mathematical relationship between torque, rotational speed, and power. Power in horsepower equals torque in lbf·ft multiplied by RPM divided by 5,252. This constant (5,252) comes from the conversion between horsepower and foot-pounds per minute. In SI units, the equivalent relationship is: power in watts equals torque in N·m multiplied by angular velocity in radians per second.
This is why engine torque and horsepower curves cross at exactly 5,252 RPM on any dyno chart plotted in lbf·ft and horsepower. Below that speed, torque is higher; above it, horsepower is higher. Understanding this relationship helps you interpret engine specifications: a truck engine might produce 2,000 N·m of torque at relatively low RPM (1,200–1,800 RPM), producing enormous pulling force but modest horsepower. A sports car engine might produce only 400 N·m but at 7,000 RPM, generating much higher power output.
Torque values in real-world context
Understanding the scale of torque values helps you calibrate your intuition. When tightening a bolt by hand — snug but not hard — you typically produce about 3–8 N·m. A typical spark plug torque specification is around 20–30 N·m. A bicycle pedal spindle is typically tightened to 35–45 N·m. The wheel lug nuts on a passenger car usually require 100–140 N·m. An oil drain plug is typically 20–45 N·m depending on the engine.
At the mechanical extreme, cylinder head bolts on a high-performance engine may require 100–200 N·m applied in multiple stages. A typical family car engine produces 150–200 N·m of peak torque from the crankshaft. A performance sedan might produce 400–600 N·m. A large diesel truck engine, particularly from manufacturers like Cummins or Caterpillar, can produce 2,000–3,000 N·m or more. Industrial gearboxes and mining equipment operate at torque levels measured in kN·m — thousands of newton-metres.
Torque wrenches and why proper torque matters
A torque wrench is a tool that allows you to apply a controlled, measured amount of torque to a fastener. The most common type is the click-type torque wrench, which produces an audible and tactile click when the preset torque value is reached. Beam-type torque wrenches have a pointer that indicates torque on a scale. Digital torque wrenches display the torque value electronically and may alert you when the target is reached.
Torque wrenches are available in different ranges. A small wrench for bicycle and electronics work might cover 0–25 N·m. A mid-range automotive wrench might cover 20–200 N·m. A heavy-duty wrench for large fasteners might cover 100–600 N·m or more. Matching the wrench range to the application is important for accuracy — a torque wrench is least accurate at the extremes of its range.
The consequences of incorrect torque are serious in both directions. Under-tightened fasteners can loosen under the vibration and thermal cycling of normal operation, leading to fluid leaks (loose oil drain plugs, loose coolant fittings), structural failures (loose suspension components), or loss of sealing (loose cylinder head bolts). Over-tightened fasteners can stretch beyond their yield point — permanently deforming the bolt so it no longer provides reliable clamping force — or strip the threads in the receiving part, which can be expensive or impossible to repair without specialised tools.
Service manuals specify fastener torque values based on the bolt diameter, thread pitch, material, and the joint design. Never guess on safety-critical fasteners: suspension components, brake callipers, wheel bearings, and engine internals all have specific torque requirements. Use the Torque Converter whenever you need to work across unit systems — for example, when following a European workshop manual with an American torque wrench calibrated in lbf·ft.
For converting speed between km/h, mph, knots, and other units, the speed converter guide covers the same principles applied to velocity.