🌗 ND Filter Exposure Calculator
Enter your base (no-filter) shutter speed and the strength of your ND filter in stops to calculate the new shutter speed needed to maintain the same exposure.
Each stop doubles the time
A neutral density filter cuts light by a whole number of stops, and the shutter has to give it all back. That makes the sum a single power of two:
new time = base time × 2^stops
ND number = 2^stops density = stops × 0.3The defaults - 1/125 s entered as 0.008, with a 10-stop ND1000 - give 0.008 × 1024 = 8.2 s. The base speed goes in as a decimal: 1/125 is 0.008, 1/500 is 0.002, 1/30 is 0.033. Filter names are the light reduction factor, so ND8 is 2³ and ND1000 is really 1024.
What each option does to 1/125
| Filter | Stops | Density | 1/125 becomes |
|---|---|---|---|
| ND8 | 3 | 0.9 | 1/16 s |
| ND64 | 6 | 1.8 | 0.5 s |
| ND1000 | 10 | 3.0 | 8.2 s |
| ND100000 | 16 | 4.8 | 524.3 s |
Stacking filters adds their stops, and the dropdown has no entry for the total, so double the answer once per extra stop: ND8 on top of ND1000 is 13 stops, which is the 8.2 s figure × 8, or 65.5 s.
Frequently asked questions
What shutter speed do I need with a 10-stop ND?
Multiply the metered time by 1024. A 1/125 s reading becomes 8.2 s, 1/500 s becomes 2.0 s, and 1/30 s becomes 33.8 s - past the 30 s limit on most cameras, so that one goes on bulb.
How many stops is an ND1000 filter?
Ten. The 1000 is the light reduction factor, rounded down from the true 1024, and it corresponds to an optical density of 3.0. An ND8 is three stops and an ND64 is six.
Why is my long exposure still a stop out?
Dark filters rarely hit their rating exactly - a 10-stop can measure anywhere from 9.3 to 11 - and metering and autofocus both struggle through the glass. Meter and focus first, fit the filter second, then bracket the result.