Flash Guide Number Calculator
Find the correct flash distance from its guide number.
Result
How to use
- Enter your values in the fields above.
- Press Calculate to see your result instantly.
- Use the Share button to copy a link to your result.
About this calculator
This calculator uses a flash's guide number (GN) to find the correct flash-to-subject distance for a given aperture (f-stop), or the aperture needed for a given distance, using the relationship GN = aperture × distance (so distance = GN / aperture, and aperture = GN / distance).
Photographers using manual flash units — especially in studio or off-camera lighting setups without TTL metering — use it to get correctly exposed shots without trial and error, since guide numbers are rated for a specific ISO and distance unit (meters or feet) printed by the manufacturer. Enter the flash's guide number and either the aperture or distance to solve for the other.
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