ND Filter Calculator
Neutral density (ND) filters reduce light entering the lens, allowing longer shutter speeds for creative motion effects such as silky waterfalls, smooth moving crowds, or light trails. Each stop of ND halves the light, doubling the required shutter time. Enter your base exposure (without the filter) and the number of stops of ND, and this calculator will give you the correct shutter speed to use with the filter attached. It also accepts ND number notation (ND2, ND64, ND1000) and converts to stops automatically.
ND filter formula
New shutter (s) = base shutter (s) x 2^(ND stops)
ND optical density factor = 2^(stops)
Example: base shutter 1/60 s (0.0167 s), 6-stop ND filter. Factor = 2^6 = 64. New shutter = 0.0167 x 64 = 1.07 seconds. For 10 stops: factor = 1,024, new shutter = 0.0167 x 1,024 = 17.1 seconds.
Common ND filter stops reference
- ND2 (1 stop): subtle effect, portrait outdoors at wide aperture
- ND4 (2 stops): slight motion softening in moderate light
- ND8 (3 stops): standard for video 180-degree rule outdoors
- ND64 (6 stops): waterfalls and streams in daylight, 1-2 seconds at f/11
- ND1000 (10 stops): 10-30 second exposures in bright daylight, smooth water and clouds
- ND100000 (16-17 stops): solar photography (with appropriate filter, do not look at the sun through an optical viewfinder)
ND filter calculator: frequently asked questions
What is an ND filter and what does it do?
A neutral density (ND) filter reduces the amount of light entering the lens without affecting color. It allows you to use longer shutter speeds or wider apertures in bright light than would otherwise be possible. Common uses include long-exposure waterfalls, silky water effects, and wide-aperture portraits in daylight.
How do ND filter stops translate to exposure time?
Each stop of ND reduces light by half, so each stop doubles the required shutter speed. An ND filter of N stops multiplies the shutter time by 2^N. An ND 3-stop filter turns a 1/500 s exposure into 1/500 x 2^3 = 1/500 x 8 = 1/62.5 s, approximately 1/60 s.
What do ND filter numbers like ND2, ND64, or ND1000 mean?
ND filter numbers indicate the optical density multiplier. ND2 passes 1/2 of the light (1 stop). ND4 = 2 stops. ND8 = 3 stops. ND64 = 6 stops. ND1000 = 10 stops. Stops = log2(ND number): 10 stops = log2(1000) = 9.97, so ND1000 is approximately 10 stops.
Can I stack ND filters?
Yes. Stacked ND filter stops add together. An ND6 (6 stops) plus ND3 (3 stops) gives 9 total stops of light reduction. However, stacking can introduce vignetting and color casts. Variable ND filters adjust from about 2 to 8 stops in a single filter.
What shutter speed do I need for silky water with an ND filter?
Silky waterfall effects typically require 1-5 seconds of exposure. If your unfiltered shutter at f/11 ISO 100 is 1/60 s in bright light, adding a 6-stop ND (ND64) gives: 1/60 x 64 = 1.07 seconds. Adding 10 stops (ND1000): 1/60 x 1024 = 17 seconds.
Official sources
- ISO 6728: Photography, Cameras, Specification of variable controls. ISO.org.
- ISO 12232:2019: Photography, Digital still cameras, Determination of exposure index. ISO.org.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.