ADC Resolution Calculator (LSB and Step Size)
By Santaji GadepatilinUpdated October 27, 2026
An analog-to-digital converter turns a voltage or current into a number, and its bit depth sets the smallest change it can see. Read analog-to-digital conversion explained and how this affects analog signal resolution in PLCs. This free ADC resolution calculator solves for whichever value you leave blank and shows the formula and steps.
How to use the ADC resolution calculator
Enter the ADC’s resolution in bits, the full-scale reference voltage and an input voltage. You get the number of levels, the step size, the digital code and the theoretical signal-to-noise ratio.
For more background, read PLC Analog Scaling from Raw Counts and ADC Working Principle.
ADC resolution formulas
LSB = Vref ÷ 2ⁿ · Code = ⌊Vin ÷ LSB⌋ · SNRideal = 6.02n + 1.76 dB
Resolution by bit depth
| Bits | Levels | LSB at 3.3 V | LSB at 5 V | LSB at 10 V |
|---|---|---|---|---|
| 8 | 256 | 12.89 mV | 19.53 mV | 39.06 mV |
| 10 | 1,024 | 3.223 mV | 4.883 mV | 9.766 mV |
| 12 | 4,096 | 0.8057 mV | 1.221 mV | 2.441 mV |
| 14 | 16,384 | 0.2014 mV | 0.3052 mV | 0.6104 mV |
| 16 | 65,536 | 0.05035 mV | 0.07629 mV | 0.1526 mV |
| 24 | 16,777,216 | 0.0001967 mV | 0.000298 mV | 0.000596 mV |
4–20 mA inputs
PLC analog cards often map 4–20 mA to a raw count range, for example:
| Card scaling | Counts per mA |
|---|---|
| 0–27,648 for 4–20 mA (Siemens S7) | 1,728 |
| 0–32,000 for 4–20 mA | 2,000 |
| 6,242–31,208 for 4–20 mA (Rockwell 16-bit) | 1,560 |
Convert counts to engineering units with the 4–20 mA scaling calculator.
Getting the best from an ADC
- Use a stable, low-noise reference — its error appears directly in every reading.
- Filter the input below half the sample rate to prevent aliasing — see the RC filter calculator.
- Average or oversample: averaging 4ⁿ samples adds about n bits of resolution when noise is present.
Frequently asked questions
What is ADC resolution?
The smallest voltage change the ADC can detect — one least significant bit (LSB) — equal to full-scale voltage ÷ 2ⁿ. A 12-bit ADC with a 3.3 V reference resolves about 0.806 mV.
What is the digital code for a voltage?
Code = floor(V_in ÷ LSB). 1.65 V on a 12-bit, 3.3 V ADC gives code 2,048.
Is more bits always better?
Only if noise and reference accuracy are good enough to use them. The effective number of bits (ENOB) is often 1–3 bits less than the nominal resolution.
What resolution do PLC analog inputs have?
Commonly 12–16 bits. A 16-bit input on 4–20 mA resolves about 0.25 µA per count when it spans 0–21 mA across 65,536 counts.