π ND Filter Calculator
Calculate the correct long-exposure shutter speed for any ND filter.
Required Exposure Time
How to Use This Calculator
Set your base shutter speed (the exposure that gives correct brightness without any filter), then select the ND filter you have. If you're stacking two filters, select the second one from the dropdown below. The result shows the new exposure time you need to set on the camera to get the same brightness you had without the filter.
Meter the scene without any filter attached. Note the shutter speed that gives correct exposure at your chosen aperture and ISO. Select that from the "Base Shutter Speed" dropdown.
Select your ND filter from the list. Common choices: ND64 (6 stops) for moderate long exposures, ND1000 (10 stops) for seconds-long exposures in daylight.
If stacking two filters, select the second filter from the optional dropdown. The calculator adds the stops together and shows the combined result.
Attach the filter, set the camera to Bulb or your calculated shutter speed, and shoot. For exposures over 30 seconds, use a cable release to avoid camera shake.
ND Filter Stops Formula
Each stop of ND filter halves the light entering the lens, so you must double the shutter speed to compensate. A 10-stop ND filter multiplies the shutter by 2 to the power of 10, which equals 1024. So 1/125s becomes about 8 seconds. Stacked filters simply add stops: a 6-stop filter combined with a 3-stop filter gives you 9 total stops. The ND factor numbers on filter labels (ND64, ND1000) correspond to how many times the light is reduced.
Real-World Examples
When You Need This
Waterfalls and rivers are the most common reason to reach for an ND filter. In bright daylight, even at base ISO and a small aperture, your fastest practical shutter speed might be 1/500s, which freezes every drop. To get that silky smooth water effect you see in landscape photos, you need 1/4s or longer. An ND64 (6-stop) filter takes 1/500s all the way to about 1/8s, and stacking it with an ND8 gets you into 1-second territory where water turns to mist.
Street photographers and architectural shooters use ND filters for a different reason: blurring people. A 3 to 6 second exposure with an ND1000 in a busy city square turns pedestrians into ghostly translucent shapes while buildings stay perfectly sharp. Any person who stands still for too long starts to appear, which creates an interesting mix of blur and detail. Calculate the exposure before you set up the tripod so you're not guessing and chimping in front of passersby.
Frequently Asked Questions
What is an ND filter?
A Neutral Density (ND) filter is a dark, optically neutral glass that reduces the amount of light entering the lens without affecting color. Used to allow slower shutter speeds in bright conditions.
What do ND filter numbers mean?
ND filters are rated by their optical density. ND2 = 1 stop, ND4 = 2 stops, ND8 = 3 stops, ND64 = 6 stops, ND1000 = 10 stops. Some are labeled by stops (e.g., "10-stop filter").
When would I use an ND filter?
Smooth silky waterfalls, blurred crowd motion, creamy sea motion, long cloud streaks, or shooting video at 1/50s in bright daylight. Any time you need a slower shutter than the light allows.
What ND filter for daytime long exposures?
A 6-stop (ND64) filter is popular for general use. A 10-stop (ND1000) allows 30-second exposures in daylight. For very long exposures (minutes), use ND1000 or stack filters.
Can I stack ND filters?
Yes β stacking adds the stops. ND64 (6 stops) + ND8 (3 stops) = ND512 (9 stops). This calculator handles stacked filters by letting you combine two filter values.