Torque Calculator

Calculate torque (τ = F × r), force, or lever arm. Includes power-RPM-torque conversion for engine and motor calculations — results in N·m and ft·lb.

N
m

Enter your values above to see the results.

Tips & Notes

  • Torque = Force × perpendicular distance. A 20 N force applied 0.5 m from a pivot produces 10 N·m. Doubling the wrench length doubles the torque — this is why breaker bars are longer than standard ratchets.
  • Power-torque-RPM relationship: Power (W) = Torque (N·m) × Angular velocity (rad/s) = Torque × 2π × RPM / 60. A 100 kW engine at 3,000 RPM produces: Torque = 100,000 × 60 / (2π × 3,000) = 318.3 N·m.
  • Unit conversions: 1 N·m = 0.7376 ft·lb = 8.851 in·lb. Engine torque is often in N·m or ft·lb; fastener torque specs are often in N·m or in·lb. Always verify units before tightening.
  • Torque wrenches measure and limit applied torque to protect threaded connections. Under-torquing causes loosening; over-torquing strips threads or stretches bolts past their elastic limit.
  • Moment of a couple: two equal opposite forces separated by distance d create a pure torque (couple) = F × d, with no net force. Steering wheels and screwdrivers apply couples, not single forces.

Common Mistakes

  • Using total arm length instead of perpendicular distance — torque uses the perpendicular component of the force times the arm length. If force is at angle θ: τ = F × r × sin(θ). A force parallel to the lever arm creates zero torque.
  • Forgetting to convert RPM to rad/s in power calculations — Power = τ × ω requires ω in rad/s. ω = 2π × RPM / 60. At 1,500 RPM: ω = 2π × 1,500 / 60 = 157.08 rad/s, not 1,500.
  • Confusing torque (N·m) with energy (J = N·m) — both have the same units but different meanings. Torque is a rotational force about an axis; energy is work done. Never add or equate them.
  • Applying torque spec in wrong units — a bolt spec of 25 ft·lb is not the same as 25 N·m (25 ft·lb = 33.9 N·m). Using the wrong unit can over- or under-torque by 36%, risking joint failure.
  • Ignoring friction in torque transmission — threaded fasteners lose 70-90% of applied torque to thread and bearing friction. Only 10-30% actually becomes bolt clamping force. Use proper lubrication and torque specs.

Torque Calculator Overview

Torque is the rotational equivalent of force — every rotating machine, threaded fastener, and lever system involves torque. The principle that τ = F × r allows engineers to trade force for distance: a small force over a long arm can produce the same torque as a large force over a short arm.

Torque formula:

τ = F × r × sin(θ) | For perpendicular force: τ = F × r | Units: N·m (SI), ft·lb (imperial)
EX: Tighten an M12 bolt with target 86 N·m. Using a 0.25 m wrench: F = 86 / 0.25 = 344 N (about 35 kg of hand force). Extend to 0.4 m breaker bar: F = 86 / 0.4 = 215 N (22 kg). Longer wrench = less force required.
Power-Torque-RPM relationship:
Power (W) = τ (N·m) × 2π × RPM / 60 | Torque = Power × 60 / (2π × RPM) = Power (kW) × 9,549 / RPM
EX: 200 kW engine at 5,500 RPM → Torque = 200,000 × 60 / (2π × 5,500) = 347 N·m. Same engine at 2,500 RPM peak torque of 420 N·m → Power at that point = 420 × 2π × 2,500 / 60 = 109.9 kW
Torque specifications — common fasteners:
Bolt SizeGrade 8.8 (Dry)Grade 8.8 (Lubricated)Grade 10.9 (Dry)
M610 N·m8 N·m14 N·m
M825 N·m20 N·m35 N·m
M1049 N·m39 N·m69 N·m
M1286 N·m69 N·m120 N·m
M16210 N·m168 N·m295 N·m
M20410 N·m328 N·m580 N·m
Engine torque and power — typical values:
Vehicle TypePeak TorqueRPM at Peak TorquePeak Power
Small economy car (1.0L turbo)170–200 N·m1,500–3,00085–100 kW
Family sedan (2.0L)250–320 N·m1,800–3,500130–160 kW
Performance car (3.0L turbo)450–600 N·m2,000–4,000280–400 kW
Heavy truck diesel2,000–3,000 N·m1,000–1,500300–450 kW
Electric motor (Tesla Model 3)420 N·m0–5,000283 kW
The power-torque-RPM relationship explains a fundamental difference between electric and combustion engines. Electric motors produce maximum torque from zero RPM — the full 420 N·m is available the instant you press the accelerator. Combustion engines must rev to a specific RPM range to develop their peak torque, which is why they require multi-speed gearboxes. This difference is the primary reason electric vehicles feel faster from a standstill despite often having similar or lower peak power figures than equivalent combustion vehicles.

Frequently Asked Questions

Torque τ = F × r × sin(θ), where F is force in Newtons, r is the distance from the pivot to where force is applied (meters), and θ is the angle between force and lever arm. For a force perpendicular to the arm (θ = 90°, sin = 1): τ = F × r. Example: a 50 N force applied at the end of a 0.4 m wrench perpendicular to the handle → τ = 50 × 0.4 = 20 N·m. Extending the wrench to 0.6 m: τ = 50 × 0.6 = 30 N·m — 50% more torque with 50% longer wrench.

Torque (N·m) = Power (W) × 60 / (2π × RPM) = Power (kW) × 9,549 / RPM. Example: 150 kW engine at 4,000 RPM → Torque = 150,000 × 60 / (2π × 4,000) = 9,000,000 / 25,133 = 358 N·m. At peak power RPM, torque can be calculated from power. Peak torque occurs at a different (lower) RPM than peak power for most engines — this is why towing vehicles need high low-RPM torque, not high peak power.

1 N·m = 0.7376 ft·lb. 1 ft·lb = 1.3558 N·m. 1 in·lb = 0.1130 N·m. Quick reference: 10 N·m = 7.4 ft·lb; 25 N·m = 18.4 ft·lb; 50 N·m = 36.9 ft·lb; 100 N·m = 73.8 ft·lb; 200 N·m = 147.5 ft·lb. Automotive lug nuts in the US are often specified in ft·lb (80-120 ft·lb for most passenger cars = 108-163 N·m). Always use a calibrated torque wrench and the manufacturer specification for critical fasteners.

Bolt torque spec depends on bolt size, grade, and lubrication state. General guideline for steel bolts, dry conditions: M8 Grade 8.8: 25 N·m; M10 Grade 8.8: 49 N·m; M12 Grade 8.8: 86 N·m; M16 Grade 8.8: 210 N·m. Lubricated (engine oil or thread lubricant) reduces required torque by 20-30%. A commonly cited rule of thumb for dry steel fasteners: T ≈ 0.2 × F_clamp × d, where F_clamp is desired clamping force and d is bolt diameter. Always use manufacturer torque specifications when available — they account for joint stiffness, gasket compression, and safety factors.

Torque produces angular acceleration in rotating systems: τ = I × α, the rotational analog of F = ma. Here I is moment of inertia (kg·m²) and α is angular acceleration (rad/s²). For a solid disk: I = ½mr². Example: a 10 kg flywheel with 0.3 m radius (I = ½ × 10 × 0.09 = 0.45 kg·m²), accelerated from 0 to 1,500 RPM (157 rad/s) in 5 seconds → α = 157/5 = 31.4 rad/s² → τ = 0.45 × 31.4 = 14.1 N·m required to accelerate the flywheel.

In everyday engineering usage, torque and moment are often used interchangeably, but there is a subtle distinction. Torque typically refers to a twisting force along an axis — what a motor delivers or a wrench applies. Moment (bending moment) typically refers to the tendency of a force to rotate a structure about a point — what a beam experiences under transverse loads. Both are calculated as Force × perpendicular distance (N·m), but torque acts about the long axis of a shaft, while bending moment acts about an axis perpendicular to the structural member. In structural engineering, moment is used; in mechanical engineering, torque is more common.