ADC Resolution Calculator

LSB size, digital code, quantisation error, ideal SNR and data rate for an N-bit ADC.

What it does

Converts between an analog voltage and the digital code of an N-bit ADC, and shows the step size (LSB), quantisation error, ideal SNR and data rate.

Where it's used

Choosing an ADC, scaling sensor readings in firmware and checking measurement resolution.

How to use it

Choose voltage → code or code → voltage.
Enter the resolution in bits and the reference voltage.
Enter the input voltage or code (decimal, 0x hex or 0b binary).
Enter the sample rate for the data rate.

The formula explained

LSB: Vref / 2ᴺ — smallest voltage step
code: ⌊Vin / LSB⌋
SNR: 6.02N + 1.76 dB for an ideal ADC
ENOB: effective number of bits for a real ADC

Worked example

An Arduino-style 10-bit ADC reading 2.5 V.

Inputs:

Convert: Voltage → code
Resolution: 10 bits
Reference voltage (full scale): 5 V
Input voltage: 2.5 V
Sample rate: 10k S/s

The calculator gives:

Digital code: 512
Binary: 1000000000
LSB size: 4.883 mV

Tips and common mistakes

Real ADCs reach a lower ENOB than the ideal figure.
Keep the input between 0 V and Vref.
Reference accuracy directly limits measurement accuracy.

Questions people ask

How is the digital code calculated?

Code = Vin / Vref × 2^N, rounded down. 2.5 V on a 5 V, 10-bit ADC gives 2.5 / 5 × 1024 = 512. Some datasheets use 2^N − 1 instead of 2^N; the difference is one step at full scale.

What is the ideal signal-to-noise ratio?

SNR = 6.02 × N + 1.76 dB for a full-scale sine wave. That is about 62 dB for 10 bits and 74 dB for 12 bits. Each extra bit adds about 6 dB.

What is ENOB?

Effective number of bits: the resolution a real ADC actually achieves once noise and distortion are counted, ENOB = (SINAD − 1.76) / 6.02. A 12-bit converter often delivers 10–11 effective bits.

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