Flash Guide Number Calculator

Compute flash guide number, aperture, and working distance with ISO correction.

Calculate guide number, distance, and aperture relation for your flash setup.

Solve forISOAperture (f)Distance (m)GN (ISO100)

Flash range updates instantly

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How does it work?

Uses GN = f × distance with ISO scaling.

Returns both ISO100 and selected ISO guide number values.

Ideal for portrait, event, and product flash setup planning.

Reduces trial-and-error before first shot.