THD / SINAD / ENOB Calculator

How the metrics relate

All of them are power sums referenced to the fundamental. THD collects the harmonics:

$$\text{THD}=10{\log }_{10}\left(\sum _{h}10^{H_h/10}\right)$$

SINAD adds the noise to the distortion:

$$\text{SINAD}=-10{\log }_{10}\left(10^{-\text{SNR}/10}+10^{\text{THD}/10}\right)$$

and ENOB converts SINAD into "how many ideal bits would behave like this":

$$\text{ENOB}=\frac{\text{SINAD}-1.76}{6.02}$$

SFDR is simply the strongest single spur. Two practical notes: a 12-bit ADC with ENOB 9.5 is normal, not broken — the datasheet ENOB is measured under ideal conditions you won't reproduce on a 2-layer board; and if THD dominates SINAD, more averaging won't help (averaging kills noise, not distortion) — fix the front-end or drop the input amplitude instead.