扭矩转换器 – Nm、ft·lb、in·lb、kg·m

What Is Torque?

Torque is a rotational force — the tendency of a force to rotate an object about an axis. It is calculated as: Torque = Force × Distance (from the pivot point). A force of 100 N applied at 1 meter from the pivot produces 100 Nm of torque.

Torque appears everywhere in engineering: engine specifications, fastener tightening, bicycle bottom brackets, door handles, and structural bolts. Understanding torque units is essential for mechanical work, as under- or over-tightening fasteners can cause failures.

The SI unit is the Newton-meter (Nm). Imperial systems use foot-pounds (ft-lb) or inch-pounds (in-lb). Older metric specifications sometimes use kilogram-force meters (kgf·m).

More precisely, torque is a vector quantity defined as the cross product of the position vector and the force vector: τ = r × F. The magnitude is τ = r · F · sin(θ), where θ is the angle between the force direction and the lever arm. Maximum torque occurs when the force is perpendicular to the lever (θ = 90°). This is why a wrench is most effective when you push at right angles to its handle.

Torque Unit Conversion Table

The table below shows exact conversion factors between all common torque units. The Newton-meter (Nm) is the SI standard defined by the International Bureau of Weights and Measures (BIPM).

Conversion factors are based on the exact definitions: 1 pound-force = 4.4482216152605 N (per NIST), 1 foot = 0.3048 m exactly, 1 kgf = 9.80665 N (standard gravity).

Quick Conversion Formulas

For the most common conversions, memorize these factors or bookmark this page:

Practical Torque Reference Values

Understanding typical torque values helps contextualize specifications:

Automotive Fastener Torque Specifications

Correct fastener torque is critical for vehicle safety. Below are common automotive torque values per SAE and manufacturer guidelines:

Always consult the vehicle-specific service manual. These are general ranges — actual specifications vary by make, model, and fastener grade. SAE Grade 5 and Grade 8 bolts have very different torque requirements for the same diameter.

Bolt Grade and Torque Relationship

Fastener strength is classified by grade (SAE) or property class (ISO/metric). Higher grades can withstand more torque before yielding:

A Grade 8 M10 bolt can safely handle roughly twice the torque of a Grade 5 M10 bolt. Never substitute a lower-grade fastener for a higher-grade specification — the consequences can be catastrophic in safety-critical applications like suspension, steering, and braking systems.

Torque vs. Power: Key Relationship

Torque and power are related but distinct. Power measures how quickly work is done; torque measures the rotational force itself.

Power (kW) = Torque (Nm) × RPM ÷ 9,549

Power (hp) = Torque (ft-lb) × RPM ÷ 5,252

This means an engine producing 300 Nm at 4,000 RPM generates: 300 × 4,000 ÷ 9,549 = 125.7 kW (168 hp). Diesel engines produce more torque at lower RPM (better for towing); gasoline engines produce more power at higher RPM (better for top speed).

The torque-power curves of different powertrains illustrate their strengths:

This is why electric vehicles accelerate so aggressively from a standstill — they deliver maximum torque instantly, without needing to build RPM like combustion engines.

Torque Wrenches: Types and Accuracy

A torque wrench is essential for any fastener where torque specification matters. Different types suit different applications:

Click-type wrenches should be recalibrated annually or after 5,000 cycles (per ISO 6789). Always store them at their lowest setting to reduce spring fatigue. Never use a torque wrench as a breaker bar — the shock loads destroy calibration.

Angular Tightening (Torque-to-Yield)

Some critical fasteners — especially cylinder head bolts and connecting rod bolts — use torque-to-yield (TTY) or torque-plus-angle methods. The bolt is first tightened to a specified torque, then turned an additional angle (e.g., 90° or 180°).

This intentionally stretches the bolt into its plastic deformation zone, achieving more consistent and higher clamping force than torque alone. TTY bolts are typically single-use — they cannot be reliably re-torqued after being stretched. The angular tightening compensates for the biggest variable in bolt tension: friction. Thread lubrication, surface finish, and plating all affect how much of the applied torque becomes actual clamping force versus friction losses. By specifying angle rather than torque for the final stage, engineers bypass friction variation entirely.

Bicycle Torque Specifications

Bicycle components — especially carbon fiber parts — are torque-sensitive. Over-tightening can crack carbon handlebars, seat posts, and steerer tubes, potentially causing catastrophic failure. Every serious cyclist should own a small torque wrench (2–25 Nm range).

Carbon assembly paste (e.g., Finish Line Fiber Grip) increases friction between carbon surfaces, allowing lower bolt torque while maintaining grip. Never use regular grease on carbon-to-carbon interfaces — it reduces friction and requires higher torque, which risks cracking the component.

Torque Measurement Units in Different Industries

Different engineering communities have adopted different default torque units, which creates confusion when working across disciplines:

When reading specifications from international sources, always verify which unit is being used. A Japanese repair manual from the 1990s might specify "10 kgf·m" which is 98.1 Nm — not 10 Nm. Confusing units in this case would result in only 10% of the required torque, leading to a dangerously loose fastener.

Electric Motor Torque Characteristics

Electric motors behave fundamentally differently from combustion engines. Understanding their torque curves is increasingly important as EVs become mainstream:

The Tesla Model S Plaid's three motors combine for 1,020 Nm (752 ft-lb) of torque available from 0 RPM. This is why it accelerates from 0 to 60 mph in under 2 seconds — a feat that requires well over 1,500 Nm at the wheels from a combustion engine due to torque converter and gearbox losses. Electric drivetrains are roughly 85–95% efficient at converting motor torque to wheel torque, compared to 75–85% for conventional automatic transmissions.