Encoder Counts and Resolution Calculator
Turn an encoder's pulses per revolution into counts per revolution, counts per inch or millimeter, resolution and the count rate your input must handle.
Encoder and mechanics
The encoder is assumed to be mounted directly on the shaft that moves the load. If a gearbox sits between them, multiply the distance per revolution by the gear ratio first.
How it works
A quadrature encoder outputs two square waves, A and B, offset by a quarter cycle. The PPR rating is the number of cycles on channel A per revolution. A controller can count the rising edges of A only (x1), both edges of A (x2), or every edge of A and B (x4). Most PLC high-speed counters and motion controllers use x4, which quadruples the resolution without changing the encoder.
distance per rev = π × diameter (wheel) or lead (screw)
counts per unit = counts per rev / distance per rev
count rate = counts per rev × RPM / 60
Worked example
A 1024 PPR encoder with x4 decoding drives a 4 in diameter wheel.
- Counts per revolution = 1024 × 4 = 4,096.
- Wheel circumference = π × 4 = 12.566 in.
- Counts per inch = 4096 / 12.566 = 325.95, or about 0.00307 in per count.
- At 600 RPM the controller sees 4096 × 600 / 60 = 40,960 counts per second.
Common questions
Does my input card keep up?
Compare the count rate with the maximum frequency of your counter input, which is listed in the module's datasheet. Remember that x4 decoding makes the controller count at four times the encoder's output frequency. A standard (non-high-speed) digital input usually cannot count fast encoder signals reliably.
PPR, CPR and lines: are they the same?
Manufacturers use the terms inconsistently. PPR and "lines" usually mean cycles per revolution on one channel. CPR often means the count after x4 decoding. Check the encoder's datasheet to be sure which one a number refers to.
Calculations are provided for convenience and education. Verify results against manufacturer data before relying on them for design or commissioning.