ND Filter Shutter Speed Calculator
Screw on a neutral-density filter and get the new shutter speed instantly — with the stops, ND number and optical density it costs you.
How it works
New shutter = base shutter × 2^stops · ND number = 2^stops · Optical density = stops × 0.3
A neutral-density filter dims the light by a fixed number of stops, and each stop doubles the exposure time needed to keep the same brightness. So the new shutter speed is the base speed multiplied by two raised to the power of the stops. The filter’s ND number (ND8, ND1000) is that same power of two, and its optical density is the stop count times 0.3 — three ways of writing the same amount of darkening. Ten stops turns a hand-held 1/250 s into a four-second exposure, which is how photographers blur water and clouds in daylight.
Worked example
A metered exposure of 1/250 s (0.004 s) with a 10-stop ND1000 filter becomes 0.004 × 2¹⁰ = 4.1 s — long enough to smooth moving water in bright sun.
Frequently asked questions
How do I read my base shutter speed as a decimal?
Divide 1 by the denominator: 1/250 s is 1 ÷ 250 = 0.004, and 1/60 s is about 0.0167. Enter that decimal, and the result is shown back as a familiar fraction.
What does ND1000 mean?
The number is roughly how much the filter divides the light — ND1000 cuts it to about 1/1000, which is 10 stops. ND8 cuts to 1/8 (3 stops), and so on; the calculator lists the common strengths.
Do I need a tripod with an ND filter?
Almost always for strong filters. Once the shutter speed passes about 1/30 s the camera must be locked down on a tripod, and long daytime exposures also benefit from a remote release to avoid shake.
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This calculator is for educational purposes. Double-check important results before acting on them.