Enter the equipment (PTO) speed (RPM) and the engine speed (RPM) into the PTO Ratio Calculator. The calculator will evaluate and display the PTO Ratio.
Related Calculators
PTO Ratio Formula
The calculator uses one of three formulas depending on the tab you select.
Find ratio (engine RPM and PTO RPM known):
Ratio = Engine RPM / PTO RPM
Find engine RPM (target PTO RPM and ratio known):
Engine RPM = PTO RPM * Ratio
Drive sizes (input shaft RPM and pulley or gear sizes known):
PTO RPM = Engine RPM * (Driver / Driven)
- Ratio: engine-to-PTO reduction, expressed as N:1.
- Engine RPM: crankshaft speed at the input side of the PTO gearbox.
- PTO RPM: speed at the output (stub) shaft.
- Driver: diameter or tooth count of the pulley or gear on the input shaft.
- Driven: diameter or tooth count of the pulley or gear on the PTO shaft.
The math assumes a fixed mechanical ratio with no slip. Use diameter or tooth count consistently for both driver and driven; do not mix the two. For belt drives, sheave pitch diameter gives a more accurate result than outside diameter.
Reference Tables
Standard PTO speeds and the engine RPM needed to reach them at common ratios.
| PTO Standard | Typical Ratio | Engine RPM at Rated PTO |
|---|---|---|
| 540 RPM (Type 1) | 3.89:1 | 2100 |
| 540E Economy | 2.96:1 | 1600 |
| 1000 RPM (Type 2) | 2.10:1 | 2100 |
| 1000E Economy | 1.60:1 | 1600 |
Shaft splines associated with each standard:
| Type | Speed | Spline | Shaft OD |
|---|---|---|---|
| Type 1 | 540 RPM | 6 spline | 1-3/8 in |
| Type 2 | 1000 RPM | 21 spline | 1-3/8 in |
| Type 3 | 1000 RPM | 20 spline | 1-3/4 in |
Worked Example
A tractor reaches 540 PTO RPM at 2100 engine RPM. The ratio is 2100 / 540 = 3.89:1, and the PTO runs at 25.7% of engine speed.
To run that same PTO at 540 RPM with a 3.89:1 ratio, the engine must turn 540 × 3.89 = 2100 RPM. Drop the engine to 1800 RPM and the PTO falls to 463 RPM, which is below the 5% tolerance most implements expect.
FAQ
Why does my PTO not hit exactly 540 at rated RPM? Manufacturers pick a ratio that gives 540 (or 1000) at the engine’s rated PTO speed, which is often below max governed RPM. Running at the wrong engine speed throws the PTO off proportionally.
Can I use tooth counts instead of pulley diameters? Yes. For chain or gear drives, use tooth counts. For belt drives, use pitch diameters. Do not mix units between the driver and driven.
What is economy PTO? A second gear ratio that hits 540 or 1000 at a lower engine RPM, used for light loads to save fuel and reduce noise.
