Shaft Power / Torque / Speed Calculator

Shaft Power / Torque / Speed Calculator

Shaft Power / Torque / Speed

CE Style

Enter any two of P, T, n

RPM
For input power estimate (P_in ≈ P_out / η)
If set, shows tangential force F and belt speed

Key Results

Mechanical Notes

Core relation: P = T · ω, with ω = 2π·n/60. Useful shortcuts (derived): T(N·m) ≈ 9550·P(kW)/n, T(lbf·ft) ≈ 5252·HP/n.

How to Use the Shaft Power / Torque / Speed Calculator

Solve any missing one of P, T or n from the other two. The tool also shows angular speed, belt force at a given radius, belt/surface speed, and input power from efficiency.

1) Pick Units & What You Know

  • Units: SI (W, N·m) or Imperial (HP, lbf·ft).
  • Decide which two of P (power), T (torque), n (RPM) you already know.
  • Use the Preset dropdown for quick examples.

2) Enter Any Two of P, T, n

  • Leave the unknown field blank.
  • The calculator solves the missing one using P = T · ω and ω = 2π·n/60.
  • You can mix units (e.g., HP with RPM; the tool converts internally).

3) Optional: Efficiency & Radius

  • η (efficiency): outputs Pin ≈ Pout/η for motor sizing and electrical load estimates.
  • Radius r (pulley/gear): gives tangential force F = T/r and belt/surface speed v = ω·r.
  • Pick units for r (mm, m, in, ft); results show both SI and Imperial force/speed.

4) Read the Results

  • Power: W, kW, HP.
  • Torque: N·m and lbf·ft.
  • Speed: RPM and angular speed ω in rad/s.
  • Input power (if η set): W, kW, HP.
  • Tangential force at radius (if r set): N and lbf; belt/surface speed: m/s and ft/min.
Core relation: P = T · ω with ω = 2π·n/60. Units are auto-handled—no manual conversions needed.

Handy Shortcuts

  • Torque (N·m) ≈ 9550 · P(kW) / n(RPM)
  • Torque (lbf·ft) ≈ 5252 · HP / n(RPM)
  • Force at radius: F = T / r
  • Belt speed: v = ω · r (m/s)
  • Mechanical input power: P_in ≈ P_out / η
  • ω: 2π·n/60 (rad/s)

Quick Checklist

  • Exactly two of P, T, n entered
  • Correct units selected for power/torque
  • RPM is under rated mechanical limits
  • Include efficiency for input power sizing
  • Set pulley/gear radius to get belt force/speed
  • Verify motor/drive continuous ratings vs duty
FAQ & Tips

Why do my HP and kW differ slightly?
The tool uses 1 HP = 745.699872 W (imperial mechanical HP). Rounding can show tiny differences.

What radius should I enter?
Use the effective radius where force is applied: pulley pitch radius, gear pitch radius, or drum radius.

Continuous vs peak?
Use continuous ratings for steady operation. Check peak/accel separately and ensure drive/motor thermal limits are met.

Direction of rotation?
Power formulas use magnitudes; sign conventions are application-specific and not required for these scalar results.

Copy-Paste Mini Workflow

1) Pick units (SI or Imperial)
2) Enter any two of: P, T, n (leave the unknown blank)
3) (Optional) Set efficiency η and radius r
4) Read the solved value, ω, input power, force at r, and belt speed
5) Confirm against motor/drive ratings and safety margins