Calculate PTO ratio, required engine RPM, or output shaft speed from pulley pitch diameters or tooth counts.

Ideal fixed-ratio speeds with no slip. Check the equipment manual for compatibility, rated speed, torque and guarding; a calculated ratio does not establish safe operation.

540 rpm preset; edit for 1000 rpm or another target.

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

Illustrative engine speeds at selected ratios; actual gearing and rated engine RPM depend on the machine.

PTO Standard Example 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.

Using the unrounded ratio 2100 / 540, 540 PTO RPM requires 2100 engine RPM. At 1800 engine RPM the PTO turns about 463 RPM. Use the equipment manual to determine the permitted operating speed; there is no universal 5% tolerance.

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.