马力扭矩计算器
This horsepower to torque calculator uses the formula HP = Torque × RPM / 5252 to solve for horsepower, torque (ft-lb or Nm), or engine speed (RPM). Choose what you want to find, enter the two known values, and get an instant result with unit conversions between HP, kW, ft-lb, and Nm.
Horsepower to Torque Calculator
Use the formula HP = Torque × RPM / 5252 to solve for horsepower, torque, or RPM. Select what you want to find, enter the two known values, and get instant results with unit conversions.
常见问题
马力和扭矩有什么区别？
扭矩（Torque）是旋转力的大小，单位为 N·m 或 lb·ft，决定了起步加速能力；马力（Horsepower）是功率的大小，等于扭矩乘以转速，决定了高速持续加速能力。两者通过公式 HP = 扭矩 × 转速 / 5252 相互关联（英制单位）。
如何将扭矩和转速换算为马力？
公式为：马力 = 扭矩(lb·ft) × 转速(RPM) / 5252；或在公制单位下：功率(kW) = 扭矩(N·m) × 转速(RPM) / 9549。1 马力 = 0.7457 kW。本计算器支持两种单位制的换算。
为什么 5252 RPM 时马力等于扭矩？
在英制单位下，5252 RPM 是马力和扭矩数值相等的特殊转速点。这源于马力的定义（1 HP = 33,000 ft·lb/min），经推导得出换算系数 5252。在这一转速以下扭矩更大，以上马力更大。
什么是公制马力和英制马力？
英制马力（hp）= 550 ft·lb/s = 745.7 W；公制马力（PS）= 75 kgf·m/s = 735.5 W。两者相差约 1.4%，欧洲汽车规格通常使用公制马力（PS），北美使用英制马力（hp）。
Understanding Horsepower, Torque & RPM
The HP = Torque × RPM / 5252 Formula
Horsepower and torque are both measures of an engine's output, but they describe different aspects of performance. Torque is a rotational force — the twisting effort the engine produces — while horsepower measures the rate at which that work is done. They are related by engine speed (RPM) through a single formula:
Horsepower Formula:
HP = Torque (ft-lb) × RPM / 5252
- HP = Horsepower (mechanical horsepower)
- Torque = Rotational force in foot-pounds (ft-lb)
- RPM = Engine speed in revolutions per minute
- 5252 = The magic constant (explained below)
The formula can be rearranged to solve for any of its three variables:
Solve for torque:
Torque = HP × 5252 / RPM
Solve for RPM:
RPM = HP × 5252 / Torque
A useful rule of thumb: at exactly 5,252 RPM, horsepower and torque (in ft-lb) are always numerically equal. Below that RPM, torque exceeds horsepower; above it, horsepower exceeds torque. This crossover point is a direct consequence of the constant 5252.
Why 5252?
The constant 5252 comes from the definition of mechanical horsepower and the conversion between linear and rotational power. Here is the derivation:
1 HP = 550 ft-lb/s (Watt's original definition)
Power = Torque × Angular velocity
Angular velocity (rad/s) = RPM × 2π / 60
HP = Torque × RPM × 2π / (60 × 550)
HP = Torque × RPM / (60 × 550 / 2π)
60 × 550 / 2π = 33,000 / (2π) ≈ 5,252.11
James Watt defined one horsepower as 33,000 foot-pounds of work per minute (or 550 ft-lb per second), based on his observations of how much work a strong horse could sustain. Dividing 33,000 by 2π (the number of radians in a full revolution) gives approximately 5,252 — the constant used in every dynamometer reading today.
HP vs Torque Curves
On a standard engine dyno chart, torque and horsepower are plotted against RPM. Several important observations apply to almost every combustion engine:
Peak Torque Comes First
Torque typically peaks at a lower RPM than horsepower. A diesel engine might produce peak torque at 1,600–2,000 RPM, making it excellent for towing and low-speed pulling. A performance gasoline engine might peak torque at 4,000–5,000 RPM. The torque curve shape determines how the car feels when accelerating from low speeds.
The Crossover Point at 5,252 RPM
Because HP = Torque × RPM / 5252, the HP and torque curves will always cross at exactly 5,252 RPM — regardless of the engine. At this point, the numerical value of HP equals the numerical value of torque (in ft-lb). This is a mathematical identity, not a coincidence, and appears on every properly measured dyno chart.
Peak HP Comes After Peak Torque
Once torque starts falling, horsepower can still rise if the rate of RPM increase outpaces the torque drop. Horsepower peaks at the RPM where the torque is falling at a rate that exactly offsets the RPM gain. Beyond that point, both torque and horsepower fall together. This is why a typical performance engine makes peak HP close to its redline.
Real-World Example: 300 HP, 300 ft-lb Engine
If an engine makes 300 ft-lb of torque at 5,252 RPM:
HP = 300 × 5252 / 5252 = 300 HP
Exactly 300 HP — confirming the crossover rule. If the same engine still makes 300 ft-lb at 6,000 RPM (unlikely but instructive):
HP = 300 × 6000 / 5252 ≈ 342 HP
Unit Conversions (HP, kW, ft-lb, Nm)
The formula above uses US customary units (mechanical horsepower and foot-pounds). Metric equivalents use kilowatts (kW) and newton-metres (Nm). Here are the key conversion factors:
| From | To | Multiply by |
|---|---|---|
| Horsepower (HP) | Kilowatts (kW) | 0.7457 |
| Kilowatts (kW) | Horsepower (HP) | 1.3410 |
| Foot-pounds (ft-lb) | Newton-metres (Nm) | 1.3558 |
| Newton-metres (Nm) | Foot-pounds (ft-lb) | 0.7376 |
The metric equivalent of the formula uses kilowatts and newton-metres:
kW = Torque (Nm) × RPM / 9549
The constant 9549 ≈ 60,000 / (2π), derived from 1 kW = 1,000 W and the same angular velocity conversion.