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ND Filter Exposure Calculator

Enter your base shutter speed and ND stops to get the new exposure.

How it is calculated

Every stop of ND filtration halves the light, so the shutter must stay open twice as long: factor = 2^stops and new exposure = base × factor. Base is the shutter speed in seconds as a decimal number (1/125 s is 0.008) and stops is how many stops the filter blocks. The tool shows the new time in seconds with two decimals, the same time split into minutes and seconds (rounded to 0.1 s first, so 119.97 s reads 2 min 0.0 s rather than 1 min 60.0 s), and the factor as a whole number followed by ×. Base must be above zero. Fractional stops such as 3.3 work, but the displayed factor is rounded to a whole number, so a filter of less than one stop shows a factor of 1× (0× appears only for negative stops). The tool does no correction for long-exposure reciprocity effects.

Worked example

Your meter reads 1/4 s (0.25) at the chosen aperture and ISO, and you add a 10-stop filter. Factor: 2¹⁰ = 1,024×. New exposure: 0.25 × 1,024 = 256.00 s. In minutes: 256 ÷ 60 = 4 full minutes and 16.0 s left over, so the tool shows 4 min 16.0 s. A 6-stop filter on 1/125 s (0.008) would give 0.008 × 64 = 0.51 s.

Try this example →

Common mistakes

  • Typing the shutter speed as a fraction (1/125) or as the denominator (125); the field takes seconds, so write 0.008.
  • Mixing up filter names and stops: an ND1000 is about 10 stops, not 1000, and the name ND8 means 3 stops; enter stops, not the optical density or the factor.
  • Setting the stops to the number of filters stacked instead of the total; two 3-stop filters together are 6 stops.
  • Trusting very long exposures blindly: the tool does no reciprocity correction, so a calculated several-minute exposure may still come out darker than expected.
  • Changing aperture or ISO after calculating; the base shutter speed must be metered at the same settings you will actually use with the filter.

About this calculator

Each stop of neutral-density filtration halves the light reaching the sensor, so the corrected shutter speed is new shutter speed = base shutter speed × 2^stops — a 6-stop ND (like an ND64) turns a 1/2-second exposure into a 32-second one, since 2^6 = 64.

Landscape and long-exposure photographers use ND filters to smooth moving water or clouds, or to allow a wide aperture in bright daylight, and this calculator lets them work out the new shutter speed before shooting rather than guessing, since many ND filters are too dark for the camera's built-in meter to read through.

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  • Editorial team

    Compare the answer with your camera's longest timed shutter setting. Many cameras stop at 30 seconds, so anything longer, such as 0.5 s through 10 stops becoming 512 s (8 min 32.0 s), means bulb mode with a remote or timer. The minutes-and-seconds line is there for setting that timer. A bright-day example at the other end: 1/250 s (0.004) with 10 stops comes to 4.10 s. Which filter strengths do you carry, and what subject do you shoot?

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