ADC Resolution Calculator
Calculate LSB voltage, SNR, dynamic range, and timing specifications for ADC configurations.
| Resolution | LSB @ Vref | SNR |
|---|
ADC (Analog-to-Digital Converter) translates continuous analog voltages into discrete digital steps.
Formulas:
- LSB (Step Size):
Vref / 2^Resolution - Theoretical SNR:
6.02 * Resolution + 1.76 dB - Conversion Time:
(Sampling Cycles + SAR Cycles) / ADC_Clock
Usage: Use this calculator to find the voltage resolution (LSB) and conversion time for your MCU. Higher oversampling improves effective resolution (ENOB) at the cost of conversion speed.
When you need it: Working out the smallest voltage an ADC can resolve (one LSB), estimating the ideal signal-to-noise ratio, or choosing how many bits you need to cover a sensor's range with margin.
Worked example: A 12-bit ADC with Vref = 3.3 V has LSB = 3.3 / 4096 = 0.806 mV. Its ideal SNR is 6.02 × 12 + 1.76 = 74 dB, and a 10 mV signal spans about 10 / 0.806 ≈ 12 codes.
Tips & gotchas:
- Effective number of bits (ENOB) is always below the nominal count once you include noise, INL/DNL and reference error — treat the datasheet's ENOB, not the bit count, as real resolution.
- Oversampling and averaging buys ~½ extra bit per 4× samples, but only if there is at least 1 LSB of noise to dither against.
- Give the sample-and-hold enough acquisition time for your source impedance, or the reading droops; add a small buffer/cap for high-impedance sensors.
- Ratiometric measurement (sensor and ADC share the same reference) cancels Vref drift entirely.
ADC resolution by bit depth
Number of steps, LSB size at 3.3 V and 5 V references, and the ideal signal-to-noise ratio 6.02 × N + 1.76 dB.
| Bits | Steps | LSB at 3.3 V | LSB at 5 V | Ideal SNR |
|---|---|---|---|---|
| 8 | 256 | 12.891 mV | 19.531 mV | 49.92 dB |
| 10 | 1,024 | 3.223 mV | 4.883 mV | 61.96 dB |
| 12 | 4,096 | 805.664 µV | 1.221 mV | 74 dB |
| 14 | 16,384 | 201.416 µV | 305.176 µV | 86.04 dB |
| 16 | 65,536 | 50.354 µV | 76.294 µV | 98.08 dB |
| 18 | 262,144 | 12.589 µV | 19.073 µV | 110.12 dB |
| 20 | 1,048,576 | 3.147 µV | 4.768 µV | 122.16 dB |
| 24 | 16,777,216 | 0.197 µV | 0.298 µV | 146.24 dB |
Frequently asked questions
What is the resolution of a 12-bit ADC at 3.3 V?
A 12-bit ADC has 2^12 = 4096 steps, so one LSB is 3.3 / 4096 = 0.806 mV.
How many bits do I need to resolve 1 mV over a 0 to 5 V range?
5 / 0.001 = 5000 steps are needed. 12 bits give 4096 steps (1.22 mV per LSB), which is not enough; 13 bits give 8192 steps (0.61 mV).
Is one LSB Vref / 2^N or Vref / (2^N - 1)?
The step size is Vref / 2^N. The highest code represents Vref − 1 LSB, not Vref itself.
Does a 16-bit ADC really deliver 16 bits?
Only an ideal one. The ideal SNR of a 16-bit converter is 6.02 × 16 + 1.76 = 98.08 dB. The usable figure is the effective number of bits, ENOB = (SINAD − 1.76) / 6.02, taken from the SINAD in the datasheet.