ND Filter Calculator

Each stop of neutral density doubles the required exposure time. Meter the scene without the filter, enter that shutter speed and the filter's strength, and the corrected time is base × 2^stops — a 1/60 s meter reading behind a 10-stop ND becomes about 17 seconds.

The number is the light-reduction factor: ND8 cuts light to 1/8 (3 stops), ND64 to 1/64 (6 stops), ND1000 to roughly 1/1000 (10 stops). Some brands label in stops or optical density instead — 0.9 density equals 3 stops. The calculator's selector covers the common namings.

Yes — stops add. A 6-stop plus a 3-stop behaves like 9 stops. The calculator has a second-filter selector for exactly this. Stacking increases the risk of vignetting on wide lenses and can add colour cast, so test your combination.

To use longer shutter speeds or wider apertures in bright light: silky waterfalls, smoothed seas, motion-blurred clouds, emptied streets, and wide-aperture portraits or video at the 180-degree shutter rule in daylight.

Compose and focus without the filter, switch to manual focus, meter and note the shutter speed, fit the filter, dial the corrected time from this calculator (Bulb mode beyond 30 s), and fire with a remote or self-timer on a solid tripod. Cover the viewfinder on DSLRs for exposures over a few seconds.

Two things drift: light changes during multi-minute exposures (especially near sunset — err longer), and strong NDs often have a slight colour cast fixable in post or with white balance. Sensor noise also rises with time; long-exposure noise reduction helps.

Real filters vary from their rated strength by up to a stop, and light changes while you shoot. Treat the calculated time as the starting point, check the histogram, and adjust by halving or doubling.

Yes — it is recorded in the EXIF metadata. Use the free EXIF viewer on this site, or the EXIF Viewer by Fluntro app on iPhone and iPad, to read shutter speed, aperture and ISO from any original photo.

No — the calculation happens entirely in your browser, and the page makes no network requests. Once loaded, it works offline, which is handy in the field.

Yes — completely free, no account. For reading the metadata of the photos you bring home, the EXIF Viewer by Fluntro app on iPhone and iPad is a one-time purchase.