This flash guide number reference table shows the aperture (f-number) for a range of guide number (gn) values, assuming a distance to subject of 5 m. Every figure is computed with the same engine that powers our Flash Guide Number Calculator, so the numbers are exact.
| Guide number (GN) | Aperture (f-number) |
|---|---|
| 10 | 2.0 |
| 20 | 4.0 |
| 30 | 6.0 |
| 40 | 8.0 |
| 60 | 12.0 |
| 80 | 16.0 |
| 120 | 24.0 |
| 200 | 40.0 |
| 280 | 56.0 |
| 400 | 80.0 |
How to use this table
Find the row closest to your guide number (gn) and read across to the aperture (f-number). For a value between two rows, the real figure sits between them — or enter your exact numbers in the Flash Guide Number Calculator for a precise answer.
Need a value that is not in the table? — the Flash Guide Number Calculator does it instantly, for free, with the formula and a worked example built in.
Related calculators
Continue exploring photography calculators with these tools: Megapixel Calculator, Crop Factor Calculator, Print Size Calculator, 35mm Equivalent Focal Length Calculator, Exposure Value Calculator.