ADC Resolution and Voltage Calculator

Convert between raw analog-to-digital converter readings and voltage, and see the smallest voltage step your ADC can resolve.

Step size (1 LSB)
Number of steps
Voltage

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How it works

An n-bit ADC divides its reference voltage into 2ⁿ steps. The size of one step, the least significant bit (LSB), is the finest voltage change it can detect.

Real ADCs also have offset, gain error and noise, and some (such as the ESP32's) are noticeably non-linear near the ends of their range, so calibrate against a known voltage for accurate measurements.

LSB = Vref / 2ⁿ
V = code × Vref / 2ⁿ
code = V / Vref × 2ⁿ

Worked example

A 12-bit ADC with a 3.3 V reference has 4,096 steps of 3.3 / 4096 = 0.806 mV. A reading of 2048 corresponds to 2048 × 0.806 mV = 1.65 V, half the reference.

Frequently asked questions

Should I divide by 2ⁿ or 2ⁿ − 1?

Both conventions are used. Dividing by 2ⁿ matches how most ADC datasheets define the LSB. The difference is one LSB at full scale and rarely matters compared with the ADC's own errors.

How do I measure voltages above the reference?

Scale them down with a resistor voltage divider first, keeping the ADC input below its reference and maximum rated voltage.

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