ND Filter Calculator — Adjusted Shutter Speed

ND filters are labelled by their filter factor (ND2, ND4, etc.) or by stops of light reduction. ND2 = 1 stop, ND4 = 2 stops, ND8 = 3 stops, and so on. Each stop doubles the required exposure time. ND1000 (10 stops) is a very popular choice for long-exposure daytime photography.

For smooth, silky water effects, you typically need a shutter speed of 1-30 seconds. An ND64 (6 stops) or ND1000 (10 stops) filter achieves this in daylight. Start with your base exposure without the filter and use this calculator to find the new shutter speed.

Yes, the stops are additive. An ND8 (3 stops) stacked with an ND64 (6 stops) gives 9 stops total (ND512 equivalent). However, stacking can cause vignetting, colour casts, and reduced image quality. A single stronger filter is usually preferable.

Optical density (OD) is the logarithmic measure of filter strength. OD = stops × 0.3. So a 10-stop filter has OD 3.0. This notation is commonly used on Lee and Formatt-Hitech filters.