Rotary Encoder Resolution Calculator
Counts per revolution, angular resolution and count rate for a quadrature encoder.
counts/rev = PPR × decoding; resolution = 360 / counts/rev; count rate = counts/rev × RPM / 60.
When you need it: Working out counts per revolution, angular resolution and speed from an incremental encoder using quadrature decoding.
Worked example: A 1024 PPR encoder with 4× quadrature gives 4096 counts/rev → resolution = 360 / 4096 = 0.088°. Speed in RPM is (counts/s) × 60 / counts_per_rev.
Tips & gotchas:
- 4× quadrature decoding quadruples resolution for free by counting every edge of both channels.
- The index (Z) pulse gives one absolute home reference per revolution for zeroing.
- Maximum count rate limits top speed — watch the hardware timer or interrupt load at speed.
- Differential (RS-422) outputs survive noise on long cables far better than single-ended ones.
Common encoder PPR values
Counts per revolution for common incremental encoder sizes. Resolution and count rate are for ×4 quadrature decoding; count rate is at 1000 RPM.
| PPR | ×1 counts/rev | ×2 counts/rev | ×4 counts/rev | Resolution (×4) | Counts/s at 1000 RPM (×4) |
|---|---|---|---|---|---|
| 12 | 12 | 24 | 48 | 7.5° | 800 |
| 20 | 20 | 40 | 80 | 4.5° | 1,333 |
| 24 | 24 | 48 | 96 | 3.75° | 1,600 |
| 100 | 100 | 200 | 400 | 0.9° | 6,667 |
| 200 | 200 | 400 | 800 | 0.45° | 13,333 |
| 360 | 360 | 720 | 1440 | 0.25° | 24,000 |
| 500 | 500 | 1000 | 2000 | 0.18° | 33,333 |
| 600 | 600 | 1200 | 2400 | 0.15° | 40,000 |
| 1000 | 1000 | 2000 | 4000 | 0.09° | 66,667 |
| 1024 | 1024 | 2048 | 4096 | 0.0879° | 68,267 |
| 2048 | 2048 | 4096 | 8192 | 0.0439° | 136,533 |
| 2500 | 2500 | 5000 | 10000 | 0.036° | 166,667 |
| 2560 | 2560 | 5120 | 10240 | 0.0352° | 170,667 |
| 4096 | 4096 | 8192 | 16384 | 0.022° | 273,067 |
Frequently asked questions
How many counts per revolution does a 20 PPR encoder give?
20 counts with ×1 decoding, 40 with ×2 and 80 with ×4 quadrature decoding. At ×4 one count is 360 / 80 = 4.5°.
Is CPR the same as PPR?
Not always. PPR is pulses per revolution on one channel. CPR is used two ways: some datasheets mean cycles per revolution (the same number as PPR), others mean counts per revolution after ×4 decoding (4 × PPR). Check which one the datasheet means before sizing a counter.
What PPR do I need for 0.1° resolution?
counts/rev = 360 / 0.1 = 3600. With ×4 decoding that is 3600 / 4 = 900 PPR; the next common size up is 1000 PPR, which gives 0.09° per count.
How fast do the counts arrive at speed?
counts/s = PPR × decoding × RPM / 60. A 2560 PPR encoder with ×4 decoding at 3000 RPM produces 2560 × 4 × 3000 / 60 = 512,000 counts per second, so the timer input or interrupt path has to keep up with that rate.