Flash Guide Number Calculator
Calculate flash exposure settings using guide numbers for manual flash photography.
Flash Settings
Maximum Flash Distance
10.36m
(34.0 ft) at f/5.6
For Subject at 5m
Required Aperturef/11.6
Required Flash Power1/8
Power StatusSufficient
Guide Number Details
Base GN (ISO 100)58m
ISO Factorx1.00
Power Factorx1.00
Effective GN58.0m
Distance vs Exposure
5.2m+2 EV
7.3m+1 EV
10.4m0 EV (max)
14.6m-1 EV
20.7m-2 EV
Guide Number Formula
GN = Distance x Aperture
• Distance = GN / Aperture
• Aperture = GN / Distance
• GN at ISO 200 = GN100 x 1.41
• At 1/2 power, GN = Full GN x 0.71