ND Filter Calculator
Get the exact shutter speed to use after screwing on any ND filter.
ND Filters Explained: Stops, Long Exposures and Stacking →
What ND filters do
A neutral density (ND) filter is dark glass that cuts the light reaching the sensor without shifting colour. It lets you use long shutter speeds in daylight - to smooth water into silk, blur moving clouds, or drop a bright scene to a workable exposure. This tool tells you the new shutter speed once the filter is on.
ND numbers, stops and exposure time
Each ND strength adds a fixed number of stops, and every stop doubles the exposure time. An ND8 is 3 stops, so it turns 1/125 s into about 1/15 s. A 10-stop ND1000 multiplies the time by 1024, turning 1/125 s into roughly 8 seconds. Enter your metered shutter speed and pick the filter to get the exact result.
Stacking ND filters
You can combine filters by adding their stops: an ND8 (3 stops) plus an ND64 (6 stops) equals 9 stops. Focus and compose first, then attach a strong ND, because very dark filters can stop the camera focusing through them. Use a tripod - the whole point is a long, blur-friendly exposure.
How this calculation works
Formula: t_new = t × 2^stops
where:
t= shutter timestops= filter strength (stops)
Sources:
FAQ
How many stops is an ND1000?
An ND1000 (a 10-stop filter) multiplies exposure time by 1024 - a 1/125 s exposure becomes about 8 seconds.
Can I stack ND filters?
Yes; add their stops together. An ND8 (3 stops) plus an ND64 (6 stops) equals 9 stops total.
How do I know how many stops my ND filter is?
The ND number tells you: ND2 is 1 stop, ND4 is 2, ND8 is 3, and it doubles each time; ND1000 is 10 stops.
Do I need to refocus with an ND filter?
Focus and compose first, then attach a strong ND filter, because very dark filters can stop the camera focusing through them.