ADC Resolution, LSB, and Voltage Calculator

Both are used. 1024 (=2^N) is faithful to the ADC transfer function, with each code representing a bin of width Vref/1024 (a reading of 1023 is 4.9951V, not exactly 5V). 1023 (=2^N−1) provides a linear mapping of 0〜Vref, where a reading of 1023 is exactly 5V. Most precisely, divide by 1024 and add an offset of +0.5LSB. You can check both results using the convention toggle in this tool.

1 LSB = Vref ÷ 2^N is the voltage per code, and quantization error is ±0.5 LSB. Dynamic range is 6.02·N dB (the ratio of full scale to 1LSB), and ideal SNR for a full-scale sine wave is 6.02·N + 1.76 dB. When you increase N by 1 bit, LSB halves and dynamic range improves by about 6dB. LSB varies with Vref and convention, but dynamic range/SNR is determined only by N.

To improve resolution by w bits, accumulate 4^w times as many samples and divide by 2^w (decimation). For example, to make 12-bit equivalent to 14-bit requires 4^2 = 16 times oversampling. However, this assumes the input has random noise of at least 1LSB (or dithering if needed); if noise is too small, the effect won't work. Effective resolution = N + w, effective LSB = Vref ÷ 2^(N+w).