Silverlog Flash

Calculate flash exposure from guide numbers. Work out the right aperture for any flash-to-subject distance, or find your maximum range.

Silverlog Flash calculates flash exposure using guide numbers — the fundamental relationship between flash power, distance and aperture.

HOW IT WORKS Enter your flash guide number, then either the distance to your subject or your desired aperture. The calculator works both ways: distance to aperture, or aperture to maximum distance. Adjust ISO to see how sensitivity affects your working range.

FEATURES • Guide number to aperture calculation • Guide number to maximum distance calculation • ISO adjustment • Metric and imperial distance units • Works offline — no internet connection needed • Clean, focused interface • Dark mode support

USEFUL FOR • Manual flash photography without TTL • Working out flash-to-subject distance for off-camera flash • Understanding your flash's effective range at different apertures • Film photographers using manual flash units • Studio photographers calculating lighting ratios

Part of the Silverlog photography toolkit. No account required. No data collected.