ND Filter Calculator

How to use

1. 1Enter the base shutter speed you metered without the filter, as a fraction such as 1/250 or a number of seconds such as 2.
2. 2Tap an ND filter preset, or tap several to stack them. Each preset shows its strength in stops, as an ND number, and as an optical density.
3. 3To use a filter not in the list, open the custom row and enter its stops, ND number, or density; the value is converted to stops automatically.
4. 4Read the long exposure shutter speed in the result panel, shown both as a readable time and as exact seconds you can dial into a timer.
5. 5If your camera only adjusts in steps, use the nearest camera step helper to round to full, half, or third stops.
6. 6For times over 30 seconds, set the camera to bulb mode with a remote or intervalometer and use a tripod. Everything runs in your browser.

About this tool

ND Filter Calculator answers the one question every long exposure shot starts with: with this neutral density filter on the lens, how long does the shutter need to stay open? A neutral density filter blocks a fixed amount of light measured in stops, and every stop halves the light reaching the sensor, so to keep the same exposure the shutter time has to double for each stop the filter cuts. The math is newExposure = baseExposure times two to the power of the total stops, and this tool does it for you, including the awkward parts. The first awkward part is naming. Filter makers print their strength three different ways and people mix them up constantly: as stops, like a 10 stop ND; as an ND number, like ND8 or ND1000, which is the light transmission divisor; and as an optical density, like 0.9 or 3.0, where 0.3 equals one stop. An ND8 filter, a 0.9 density filter, and a 3 stop filter are all the same thing. The preset grid covers the filters photographers actually buy, from ND2 up through ND64000, each labeled with all three notations, and a custom row accepts any one of the three and converts it to stops for you. The second awkward part is stacking. Screwing two filters together adds their stops, so an ND8 plus an ND1000 gives 13 stops, and this tool lets you tap several presets at once and sums them. The third awkward part is the base shutter speed itself, which is metered as a fast fraction like 1/250 for bright scenes and a plain number like 2 for dim ones; the input accepts fractions, decimals, and seconds, and the result is shown the way you would actually set it, as a 1/x fraction while still faster than a second, then in seconds, then in minutes for the long stacks. Because real cameras only adjust the shutter in fixed increments, the result also shows the nearest setting rounded to full, half, or third stops, and it flags any exposure longer than 30 seconds so you know to switch to bulb mode with a remote release and a tripod. A reference chart rounds it out, showing the resulting time for common base speeds across the most used filter strengths, so you can plan a shoot at a glance. Everything is computed in your browser from the values you enter. Nothing is uploaded, logged, or sent anywhere.

Free to use. Works in your browser. No signup, no login.