How do I calculate torque from power and speed?

Torque (Nm) = 9549 × Power (kW) / Speed (RPM). This is derived from the fundamental relationship P = T × ω, where ω = 2πn/60. The constant 9549 simplifies the calculation: 60000/(2π) ≈ 9549.

What is the relationship between kW and Nm?

Power in kW and torque in Nm are related through rotational speed: P = T × n / 9549. At any given speed, higher torque means higher power. At constant power, torque decreases as speed increases (inverse relationship).

What is the 9549 constant?

The constant 9549 comes from the unit conversion: 9549 ≈ 60000/(2π). It appears when converting between kW, Nm, and RPM. The exact value is 9549.2966... Using P(kW) = T(Nm) × n(RPM) / 9549.

How do I convert kW to hp?

1 kW = 1.341 hp (mechanical horsepower). Conversely, 1 hp = 0.7457 kW. This is the mechanical (imperial) horsepower. Metric horsepower (PS) is slightly different: 1 PS = 0.7355 kW.

Does torque change with speed?

For a given power source, yes. Electric motors have a rated torque at rated speed. At constant power output, torque is inversely proportional to speed: T = 9549 × P / n. However, actual motor torque curves vary — induction motors have peak torque (breakdown torque) at a specific slip speed.

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扭矩 — 功率 — 轉速計算器

在扭矩、功率與轉速之間進行轉換。提供任意兩個參數，即可計算第三個。支援 kW、Nm、RPM 並提供英制單位轉換。

kW ↔ Nm ↔ RPM hp & ft·lbf T = 9549 × P / n

結果

計算結果

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扭矩

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功率

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轉速

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角速度 ω

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功率 (英制)

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扭矩 (英制)

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基本關係

功率、扭矩與轉速之間的關係為：

其中 ω = 2πn/60 為以 rad/s 為單位的角速度，n 為以 RPM 為單位的轉速。

實用公式（含常數 9549）

代入並重新排列以求解各未知數，使用常數 9549 ≈ 60000/(2π)：

單位轉換

從	至	係數
kW	hp (機械)	× 1.341
hp	kW	× 0.7457
Nm	ft·lbf	× 0.7376
ft·lbf	Nm	× 1.3558
RPM	rad/s	× 2π/60

實務範例

範例 — 1500 RPM 下的 15 kW 馬達

已知： P = 15 kW, n = 1500 RPM

T = 9549 × 15 / 1500 = 95.49 Nm

ω = 2π × 1500 / 60 = 157.08 rad/s

功率 (hp)：15 × 1.341 = 20.12 hp

扭矩 (ft·lbf)：95.49 × 0.7376 = 70.44 ft·lbf

💡 常數 9549： 這個方便的數值等於 60000/(2π) ≈ 9549.2966。它免去了將 RPM 明確轉換為 rad/s 的需要。當功率單位為 kW、扭矩單位為 Nm、轉速單位為 RPM 時適用。