Manual Flash Calculator (Free Edition) provides a handy utility for accurately determining flash-subject distance. It's quick and easy to use for tricky lighting situations where TTL auto-flash can often struggle.
This app is ad-free, and requires no special device permissions.
• Aperture range F/1.2 to F/22
• ISO range ISO50 to ISO6400
• Flash output ratios to 1/256 power
• Flash exposure compensation to 5 EV
• Zoom support for unlimited guide settings
• Power increments in 1/3, 1/2 or Full stops
• Macro closeup distances (in and cm)
Set the guide number/zoom coverage, power-ratio limit, power adjustment interval, and guide number units for your flash. (You can find this information from the guide number table in your flash user manual).
If you own more than one flash unit, please consider upgrading to Manual Flash Calculator Professional. It supports an unlimited number of flash configurations, and costs less than the price of a cup of coffee!