# Encoder counts, distance per tick and odometry calculator

> Calculate encoder counts per wheel revolution and millimetres per count for robot odometry, with quadrature decoding and gear ratio.

Canonical: https://roboticsengineering.in/encoder-counts-per-wheel-distance-calculator/ | Published: 2026-11-03 | Updated: 2026-11-04

**Distance per count is the wheel circumference divided by the counts per wheel revolution.** Enter the encoder, gearbox and wheel to get the numbers your odometry code needs.

Encoder pulses per motor revolution (per channel)Decoding (1, 2 or 4)Gear ratio (N : 1)Wheel diameter (mm)

Counts per wheel revolution: **–**Distance per count: **–** mmCounts per metre: **–**

Measure the real counts by turning the wheel by hand ten times. Gear backlash and tyre squash change the result.

## How it is calculated

Counts per wheel revolution = encoder pulses per motor revolution × decoding factor × gear ratio. Distance per count = π × wheel diameter ÷ counts per wheel revolution. Decoding is 4 when your code counts both edges on both channels of a quadrature encoder.

## A worked example

A motor encoder with 11 pulses per revolution, read at 4× decoding through a 30:1 gearbox gives 11 × 4 × 30 = 1,320 counts per wheel revolution. A 65 mm wheel travels π × 65 = 204.2 mm per turn, so each count is 204.2 ÷ 1,320 = 0.1547 mm, or about 6,464 counts per metre.

## Common mistakes

- Counting only one channel and forgetting the decoding factor.
- Putting the encoder after the gearbox and still multiplying by the gear ratio.
- Using the wheel diameter without allowing for the tyre squashing under load.

## Related

[wheel speed calculator](https://roboticsengineering.in/wheel-speed-rpm-calculator/), [gear train calculator](https://roboticsengineering.in/gear-train-calculator/), [ROS 2 for beginners](https://roboticsengineering.in/ros2-tutorial-beginners/).

Last reviewed: November 2026. The calculator runs in your browser and sends nothing anywhere. Results are ideal-case figures; add margin before you order parts.

## Another worked example

An encoder gives 16 pulses per motor revolution on each channel, read at 2× decoding, through a 50:1 gearbox, on an 80 mm wheel.

- Counts per wheel revolution = 16 × 2 × 50 = 1,600.
- Wheel circumference = π × 80 = 251.33 mm.
- Distance per count = 251.33 ÷ 1,600 = 0.1571 mm.
- Counts per metre = 1,600 ÷ 0.25133 = 6,366.
- If the code reads 3,200 counts, the wheel moved 3,200 × 0.1571 = 502.7 mm.

## From counts to heading

For a two-wheel robot with track width b, the change in heading is (right distance − left distance) ÷ b radians. If the right wheel travels 100 counts more than the left, that is 100 × 0.1571 = 15.71 mm. With a 200 mm track, the turn is 15.71 ÷ 200 = 0.0785 rad, or about 4.5 degrees. Forward distance is the average of the two wheel distances.

## Assumptions and limits

- Pulses per revolution is quoted differently by different sellers: per channel, or already as counts. Check the datasheet or rotate the shaft one turn and count in code.
- Odometry drifts. Wheel slip, uneven floors and a wrong wheel diameter add error that grows with distance, so correct it with other sensors when you can.
- If the encoder is on the wheel shaft rather than the motor shaft, leave out the gear ratio.

## Common mistakes

- Reading with interrupts on one channel and assuming 4× decoding.
- Using a counter variable that is too small and overflows on a long run.