About the ND Filter Calculator
This ND filter calculator gives you the correct shutter speed once a neutral density filter is on the lens. Meter the scene without the filter, enter that shutter speed, choose your filter — or two stacked filters — and the calculator multiplies the exposure by the filter factor. It shows the result as a familiar shutter setting such as 8 s or 2 min 8 s, ready to dial into bulb mode.
It is built for landscape and seascape photographers smoothing water and clouds, architectural shooters removing people from busy scenes, and videographers holding a cinematic shutter angle in bright light. Because manufacturers label filters three different ways (ND1000, ND 3.0 and 10-stop all mean the same thing), every option shows the factor, optical density and stops together.
Every stop of filtration doubles the exposure time, so the numbers climb fast: a 10-stop filter turns 1/125 s into about 8 seconds. Keep ISO and aperture the same as your metered exposure, and for exposures of several minutes consider bracketing slightly longer, since very dense filters and sensor heat can affect the result.
How to use the nd filter calculator
- 1Compose and focus without the filter, then meter the scene.
- 2Select the shutter speed your camera suggested at your chosen ISO and aperture.
- 3Pick your ND filter, and a second filter if you are stacking two.
- 4Fit the filter, set the new shutter speed (Bulb for over 30 s) and keep ISO and aperture unchanged.
- 5Check the histogram and adjust by a third of a stop if needed.
Formula and method
Each stop halves the light reaching the sensor, so to keep the same exposure the shutter must stay open twice as long per stop. The new time is the metered time multiplied by the filter factor, 2 raised to the number of stops. Stacked filters add their stops (and multiply their factors).
Optical density is the base-10 logarithm of the factor, so every 0.3 of density is almost exactly one stop. That is why ND 3.0 and ND1000 are the same filter: 10^3 = 1,000, which is 9.97 stops. In practice these filters are sold and used as 10-stop filters, so this calculator treats them as exactly 10 stops (a 1,024× factor); the 2.4% difference is far smaller than real-world filter tolerance.
- t
- Metered shutter speed without a filter (s)
- t_ND
- Shutter speed with the filter (s)
- stops
- Total filter strength in stops
Worked examples
10-stop filter at 1/125 s
A 10-stop filter multiplies exposure by 2¹⁰ = 1,024. 1/125 s × 1,024 = 8.19 s, so set about 8 seconds — enough to blur waves into mist.
6-stop filter at 1/60 s
Six stops is a 64× factor (ND 1.8). 64 ÷ 60 = 1.07 s, which softens a waterfall while keeping some texture.
ND1000 stacked with ND8 at 1/4 s
Stacking 10 + 3 stops gives 13 stops, a factor of 8,192. 0.25 s × 8,192 = 2,048 s, or 34 minutes 8 seconds in Bulb mode — enough to turn moving clouds into streaks.
Frequently asked questions
How do I calculate shutter speed with an ND filter?+
Multiply your metered shutter speed by 2 for every stop of the filter. A 6-stop filter multiplies by 64 and a 10-stop filter by 1,024, so 1/125 s becomes about 1/2 s or 8 s respectively.
Is ND1000 the same as a 10-stop filter?+
Yes, for practical purposes. ND1000 means 1/1,000 of the light gets through, which is 9.97 stops and optical density 3.0. Photographers and manufacturers call it a 10-stop filter.
What do ND 0.3, 0.6 and 0.9 mean?+
They are optical densities. Each 0.3 equals one stop, so ND 0.3 is 1 stop (ND2), ND 0.6 is 2 stops (ND4) and ND 0.9 is 3 stops (ND8).
Which ND filter should I buy first?+
A 6-stop and a 10-stop filter cover most landscape needs: 6 stops for blurring waterfalls and rivers, 10 stops for silky seas and streaking clouds in daylight. Variable NDs are popular for video.
Do I need to change aperture or ISO when adding an ND filter?+
No. Keep the aperture and ISO from your metered exposure and change only the shutter speed. Changing either would mean recalculating from a new base exposure.