Neutral Density Filter Stops Calculator
A neutral density filter cuts the light reaching your sensor so you can use a longer shutter speed in bright conditions, the key to silky water and streaking cloud effects. Because each photographic stop halves the light, the required shutter time grows as a power of 2. Enter your base shutter speed (in seconds) and the filter strength in stops, and this calculator returns the exposure factor, the new shutter time in seconds, and the same time in minutes. The math follows directly from the definition of a stop, so the result is exact.
ND filter exposure formula
Exposure factor = 2 ^ stops
New shutter (seconds) = base shutter * exposure factor
New shutter (minutes) = new shutter seconds / 60
Equivalent ND number = 2 ^ stops
One photographic stop is a doubling of light by definition, so reducing light by N stops multiplies the required shutter time by 2 to the power of N. The exposure factor and the ND number are the same value for a pure neutral density filter.
ND filter quick reference
- ND2 is 1 stop, ND4 is 2 stops, ND8 is 3 stops.
- ND64 is 6 stops, a common choice for daytime long exposures.
- ND1000 is about 10 stops and turns a fast shutter into seconds.
- Optical density 0.3 equals 1 stop; density 3.0 equals 10 stops.
- Hold aperture and ISO fixed; this tool recovers light through shutter time only.
ND filters: frequently asked questions
What does a neutral density filter do?
A neutral density (ND) filter reduces the amount of light reaching the sensor without changing color. This lets you use slower shutter speeds or wider apertures in bright light, for effects like motion blur in water or clouds, or shallow depth of field outdoors.
How do ND filter stops relate to shutter speed?
Each stop of light reduction halves the light, so it doubles the required shutter time to keep the same exposure. A 1-stop filter doubles your shutter time, a 3-stop filter multiplies it by 8 (2 to the power of 3), and a 10-stop filter multiplies it by 1,024 (2 to the power of 10).
How are ND filter numbers like ND8 or ND1000 related to stops?
The ND number is the exposure factor: ND8 reduces light by a factor of 8, which is 3 stops (since 2 cubed is 8). ND1000 is about 10 stops (2 to the power of 10 is 1,024). Optical density on some filters is the base-10 logarithm of that factor, so density 0.9 equals 3 stops.
Why does the exposure factor equal 2 to the power of stops?
A stop is a doubling or halving of light by definition. Reducing light by N stops means dividing the light by 2 to the power of N, so to keep exposure constant you multiply the shutter time by 2 to the power of N. This is a self-evident definition of a photographic stop, not an empirical estimate.
Should I adjust ISO or aperture instead?
You can compensate for an ND filter by lengthening shutter time, raising ISO, or opening the aperture, in any combination. This calculator assumes you hold aperture and ISO fixed and recover the lost light entirely through a longer shutter time, which is the most common use of strong ND filters.
Official sources
- U.S. National Institute of Standards and Technology: SI units and physical quantities.
- International Organization for Standardization: ISO 12232 photographic exposure standard.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.