ND Filter Calculator
Work out the long-exposure shutter speed for any ND filter, stack filters, or find the filter you need.
Exposure with an ND filter
Working the other way round? Jump to which filter do I need.
Pick a filter — the long-exposure time updates as you type.
- New shutter speed
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- Exact time
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- Total light loss
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Filter details
- Filter factor
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- Optical density
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- Combined filter
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Longer than 30 s — most cameras need Bulb mode and a remote release or intervalometer for this exposure.
Which ND filter do I need?
Work backwards: from the metered speed to the exposure you actually want.
- Stops needed
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- Closest filter
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- Exposure with that filter
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How it works
A neutral-density filter darkens the whole frame evenly, so you keep your aperture and ISO but
can leave the shutter open far longer. Each stop of ND halves the light, so the
corrected shutter time is simply new time = metered time × 2stops.
With a 10-stop ND1000 on a metered 1/125 s, that is 0.008 s × 1024 = 8.192 s.
Stacking filters adds their stops together (ND8 + ND64 = 3 + 6 = 9 stops = 512×), and the
optical density printed on the ring follows density = stops × 0.30103 — so 10
stops is a density of 3.0.
Filter names are nominal rather than exact: an "ND1000" is really 210 = 1024×, and
an "ND100" is about 6⅔ stops. This calculator uses the true stop value of each filter, shows
the exact time in seconds, and warns you when the exposure passes the 30-second limit where
most cameras switch to Bulb. The reverse panel takes your metered speed and the shutter time
you want and returns stops = log₂(wanted ÷ metered) plus the nearest filter that
gets you there. Digital sensors do not suffer reciprocity failure, but film does — add extra
time per your film's data sheet for exposures beyond about a second. Everything is plain
arithmetic running in your browser: no uploads, no sign-up, no ads.
Frequently asked questions
How do I calculate the shutter speed with an ND filter?
Multiply your metered shutter time by 2 to the power of the filter's stops: new time = metered time × 2^stops. A 10-stop ND1000 on a metered 1/125 s gives 0.008 s × 1024 = 8.192 s, so about 8 seconds.
How many stops is an ND1000 filter?
Ten stops. Filter names are nominal. An ND1000 really blocks 2^10 = 1024× the light, which is an optical density of 3.0 (density = stops × 0.30103). ND8 is 3 stops, ND64 is 6 stops and ND100 is roughly 6⅔ stops.
Can I stack two ND filters?
Yes. Stacked filters add their stops together, so ND8 (3 stops) plus ND64 (6 stops) equals 9 stops, or 512×. This calculator lets you stack two filters and add extra stops for a variable ND or polariser. Watch for vignetting and colour casts when stacking on wide lenses.