ADC resolution calculator
Enter the bit count and reference voltage of an analog-to-digital converter to get the voltage of one step (LSB). Then turn a reading into volts, or a voltage into the code the converter will return.
Runs in your browser: nothing you enter is sent anywhere.
How to use
- Enter the resolution in bits (8, 10, 12, 16 …) and the reference voltage.
- Choose Code to voltage to turn a reading into volts, or Voltage to code to see which code an input gives.
- Read the step size, the converted value and the range of codes.
- number of codes = 2^n, from 0 to 2^n − 1
- step size: 1 LSB = Vref / 2^n
- code → voltage: V = code × LSB (the lower edge of that code’s step)
- voltage → code: code = floor(V / LSB), kept between 0 and 2^n − 1
- ideal SNR = 6.02 × n + 1.76 dB
Worked examples
A 12-bit ADC with a 3.3 V reference (the default values): 2^12 = 4,096 codes, so 1 LSB = 3.3 / 4096 = 0.8057 mV. The reading 2048 is 2048 × 0.0008057 = 1.65 V, half of the reference. The highest code, 4,095, is 3.2992 V. The ideal SNR is 6.02 × 12 + 1.76 = 74 dB.
A 10-bit ADC with 5 V: 1 LSB = 5 / 1024 = 4.8828 mV, and 2.5 V gives the code 2.5 / 0.0048828 = 512.
Tips
- The accuracy of the result is limited by the reference: a 1 % error in Vref is a 1 % error in every voltage.
- To measure a voltage above Vref, scale it down with a voltage divider and multiply the result back.
- Extra bits help only if noise is below one step: at 16 bits and 2.5 V one step is 0.0381 mV.
Frequently asked questions
How is the step size calculated?
1 LSB = Vref / 2^n. A 12-bit ADC with a 3.3 V reference has 4,096 codes, so one step is 3.3 / 4096 = 0.8057 mV.
Should I divide by 2^n or by 2^n − 1?
This calculator uses Vref / 2^n, the convention of most ADC datasheets, where the top code 2^n − 1 sits one step below Vref. Some code divides by 2^n − 1 so that the top code reads exactly Vref; the difference is one LSB at full scale.
Why does the code come out lower than I expected?
An ADC truncates. Every voltage from code × LSB up to just below (code + 1) × LSB returns the same code, so the calculator rounds down. Voltages at or above Vref return the highest code, negative ones return 0.
What is the ideal SNR?
The signal-to-noise ratio a perfect n-bit converter reaches with a full-scale sine wave, limited only by quantisation: 6.02 × n + 1.76 dB. Real converters reach less; datasheets give it as ENOB or measured SNR.