Free Online Calculators
Base exposure + ND filter → new exposure time
Whether you're shooting silky waterfalls, busy city streets, or cinematic video, ND filters are an essential tool in any photographer's kit. But calculating the correct new exposure time after adding a neutral density filter can be tricky. Our free ND filter calculator does the math for you in seconds — no equations required.
A neutral density (ND) filter is a piece of darkened glass or resin that attaches to the front of your lens. It reduces the amount of light entering the camera evenly across all wavelengths without affecting color balance. This allows photographers to use slower shutter speeds, wider apertures, or lower frame rates than would otherwise be possible in bright conditions.
ND filters are rated by their ND factor (ND2, ND4, ND8, ND64, ND1000) or by stops of light reduction. The higher the number, the more light is blocked.
Using the calculator is straightforward. You only need two pieces of information:
The calculator instantly outputs your new, correct shutter speed. For example, if your base exposure is 1/250s and you're using an ND64 filter (6 stops), the new exposure time is approximately 1/4 second (0.25s).
Each stop of ND filtration doubles the required exposure time. The formula is:
New Exposure Time = Base Exposure Time × 2ⁿ
where n is the number of stops. An ND1000 filter is approximately 10 stops: 2¹⁰ = 1024. So a base exposure of 1/100s becomes 1024/100 ≈ 10 seconds. Our calculator handles this instantly, presenting the result in a human-readable format.
Standing before a mountain waterfall, your meter reads 1/400s at ISO 100, f/11. To get that silky smooth water effect, you want an exposure of 2–5 seconds. Using an ND1000 filter (10 stops): 1/400 × 1024 ≈ 2.6 seconds. Mount your camera on a tripod, use a remote shutter, and you're set.
You want to photograph a busy plaza and make all foot traffic invisible. Current reading: 1/250s. With an ND64 filter (6 stops): 1/250 × 64 = 0.26 seconds. Any person walking through the frame will leave only a ghost-like trace, or vanish entirely.
Filming at 24fps requires a shutter speed of 1/48s per the 180-degree rule. On a sunny day, your correct exposure is 1/2000s — far too fast. An ND filter with 5–6 stops brings you back into the correct range: 1/2000 × 64 = 1/31s, close to 1/48s.
The ND factor tells you how many times the light is reduced (ND64 = 64×). Stops tell you how many times the light is halved. ND64 equals 6 stops because 2⁶ = 64. Our calculator accepts both formats for your convenience.
Yes! When stacking filters, simply add the stops together. Two ND8 filters (3 stops each) equal 6 stops total — equivalent to one ND64. Be aware that stacking multiple filters can cause vignetting, especially on wide-angle lenses.
Budget ND filters often don't perform exactly at their stated rating. A labeled ND1000 might actually deliver between 9.5 and 10.5 stops. Use the calculator as a starting point and bracket your exposures to find the perfect shot.
Absolutely. As long as you know the current stop value of your variable ND filter (usually indicated on a scale on the filter ring), you can enter it directly into the calculator.
Rarely. ND filters are primarily used in bright outdoor conditions where you need to reduce light to achieve creative effects. Indoors, you typically need more light, not less.