Calculate SNR gain from stacking multiple astrophotography exposures and find total imaging time needed.
Enter your single exposure length in seconds, the number of frames you intend to stack, and your camera's ISO setting. The calculator returns total integration time, the SNR improvement factor, and an equivalent ISO.
Random noise averages out as frames accumulate, so signal-to-noise grows with the square root of the frame count: 30 stacked frames improve SNR about 5.5 times over a single shot, while doubling any stack adds only another 41%.
Returns diminish quickly — quadrupling frames is needed for each doubling of SNR. The effective ISO output (ISO ÷ frames) expresses the same idea from the noise side: 30 frames at ISO 800 behave roughly like a single ISO 27 exposure.
Signal-to-noise improves with the square root of the frame count: 4 frames double it, 16 frames quadruple it, and 100 frames give a tenfold gain. The calculator reports this multiplier along with the total integration time your plan represents.
For the same total time, the square-root statistics are similar once each sub is long enough to swamp read noise. Longer subs help very faint targets but risk tracking errors and satellite trails, so many imagers pick the shortest workable sub and maximize the count.
Averaging N frames cuts random noise like shooting a single frame at ISO divided by N. Stacking 16 frames shot at ISO 1600 yields noise comparable to one ISO 100 exposure — a way for DSLR users to relate stacking gains to familiar settings.
Because the gain follows √N, each doubling of the frame count adds only about 41% more SNR. Going from 25 to 100 frames doubles your SNR, but doubling it again would demand 400 frames — at some point, more integration on a new target pays off more.