ND filter calculator
Enter a base shutter speed and any ND filter to see the resulting exposure - or work backwards from the long exposure you want to the ND strength you need.
Exposure
Type any value, e.g. 0.0167 s for 1/60 s.
Result
Adjusted exposure
New speed = base × factor. Long results are shown in minutes and hours.
How it works
An ND (neutral density) filter blocks light evenly across the frame, so it simply multiplies the exposure time you would otherwise use. The filter’s label gives its optical density factor, and its strength in stops is the base-2 logarithm of that factor:
Working backwards, the number of stops between two shutter speeds tells you exactly how strong a filter to reach for:
Example
Your unfiltered shot meters at 1/60 s and you screw on an ND64 (6 stops, factor 64). New speed = (1/60) × 64 ≈ 1.07 s. To instead reach 30 s from 1/60 s you need log₂(30 ÷ 0.0167) ≈ 10.8 stops - the nearest single filter is an ND2000 (~11 stops, giving ~33 s).
Handy ND references
- ND8 (3 stops) - slight motion blur on water in daylight.
- ND64 (6 stops) - classic for silky waterfalls around 1 s.
- ND1000 (~10 stops) - 30-second-plus daytime long exposures.
- ND4000 / ND64000 (12–16 stops) - minutes-long exposures even at midday.
Related tools
Plan the full minute-by-minute capture with the long exposure calculator, balance the resulting exposure with the exposure triangle calculator, or check you can handhold the base shot with the shutter speed calculator.
Frequently asked questions
How do I work out the shutter speed with an ND filter?
Multiply your unfiltered shutter speed by the filter's optical density factor. An ND64 filter has a factor of 64 (6 stops), so a base speed of 1/60 s becomes 1/60 × 64 = about 1.07 seconds.
How many stops is my ND filter?
Stops = log2(factor). ND2 = 1 stop, ND4 = 2, ND8 = 3, ND16 = 4, ND32 = 5, ND64 = 6, ND1000 is about 10 stops, and ND4000 about 12 stops.
What ND strength do I need for a long exposure?
Decide the shutter speed you want, divide it by your unfiltered speed and take log2 of the result to get the stops you need. For example going from 1/4 s to 30 s needs log2(120) ≈ 6.9 stops, so an ND128 (7 stops) gets you to about 32 s.
Are ND stop labels exact?
Mostly yes, but some makers label by measured density so an "ND400" or "ND500" can sit slightly off a clean power of two. Use the filter's real measured density when precision matters.