ADC Resolution Calculator — LSB, SNR and effective bits

Step size, ENOB, quantisation noise and SNR for a given ADC bit depth and reference voltage.

Example: A 12-bit ADC with a 3.3 V reference resolves 805.7 µV per step across 4,096 codes, for an ideal SNR of 74 dB.

Inputs

Resolution(bits)

Reference voltage(V)

Input voltage (optional)(V)

Shows the code this voltage converts to.

ENOB (optional)(bits)

The effective number of bits from the datasheet. Usually 1–2 below nominal.

Result

LSB (step size)

805.7 µV

Total codes: 4,096
Ideal SNR: 74 dB
Quantisation noise (RMS): 232.6 µV
Full-scale input: 3.299 V

This is the ideal figure. Real converters lose 1–2 bits to noise, so a nominal 12-bit ADC often delivers 10–11 effective bits. Enter the datasheet ENOB above to see the difference.
Accuracy is capped by the reference, not the converter. A 12-bit reading from a reference with 1% error is no better than 1% however many codes it reports.

Step size at this reference (3.3 V)

Bits	Codes	LSB	Ideal SNR
8	256	12.89 mV	49.9 dB
10	1,024	3.223 mV	62 dB
12	4,096	805.7 µV	74 dB
14	16,384	201.4 µV	86 dB
16	65,536	50.35 µV	98.1 dB
18	262,144	12.59 µV	110.1 dB
24	16,777,216	196.7 nV	146.2 dB

Check it against real silicon

Chiprun runs your firmware on an emulated microcontroller and hands back the UART output, so you can confirm these numbers rather than trusting them.

Chiprun docs

Formula

LSB = V_ref / 2^N    SNR = 6.02N + 1.76 dB

Worked example

A 12-bit ADC with a 3.3 V reference resolves 805.7 µV per step across 4,096 codes, for an ideal SNR of 74 dB.

LSB = V_ref / 2^N
LSB = 3.3 V / 2^12
LSB = 805.7 µV
4,096 distinct codes across the range.
SNR = 6.02N + 1.76 dB
SNR = 6.02 × 12 + 1.76
74 dB
Each extra bit is worth about 6 dB — one more bit halves the step size.

Frequently asked questions

What is the LSB of a 12-bit ADC?

The reference voltage divided by 4096. With a 3.3 V reference that is about 806 µV per step. The LSB is the smallest voltage change the converter can distinguish, at least in principle.

Where does 6.02N + 1.76 dB come from?

Quantisation error is uniformly distributed across one LSB, giving an RMS of LSB/√12. Comparing a full-scale sine wave against that noise yields exactly 6.02N + 1.76 dB. It is why each additional bit is worth about 6 dB.

Why does my 12-bit ADC only give me 10 stable bits?

Noise. Thermal noise, reference noise, supply ripple and layout coupling all add to the signal, and the bottom bits end up random. That is what ENOB measures. Averaging N samples recovers about log₂(√N) bits — sixteen samples buys you two.

Does a better ADC give me a more accurate measurement?

Only up to the reference. Resolution and accuracy are different things: a 16-bit converter running from a reference with 1% error still gives you a 1% measurement, just expressed with more digits. Fix the reference before adding bits.

Related tools

Voltage Divider Calculator

Compute divider output voltage, or pick the best E24/E96 resistor pair for a target ratio — including the error your load introduces.

Components

Op-Amp Gain Calculator

Gain and resistor selection for inverting, non-inverting, differential, summing and instrumentation amplifier topologies.

Circuits

Nyquist & Sampling Rate Calculator

Minimum sample rate, alias frequencies and anti-alias filter requirements for a given signal.

RF & Signals

Wheatstone Bridge Calculator

Bridge output voltage and balance condition, with a strain-gauge mode.

Circuits

Hex, Binary & Decimal Converter

Convert between hex, binary, decimal, octal and ASCII, with width-aware bit grids and endianness swapping.

Firmware

Bitwise Operation Calculator

AND, OR, XOR, NOT and shifts with a live bit grid so you can see exactly which bits moved.

Firmware