Which ND Filter Do I Need?
An ND (neutral density) filter reduces light by a fixed number of stops so you can use longer shutter speeds in bright conditions. This calculator answers the buying question: given your current exposure and the shutter time you want, exactly how many stops do you need — and which filters to buy.
Your situation
Or skip the preset and type your own metered exposure below.
Result
How to use this ND filter calculator
Pick the closest scene preset, or type the shutter time you'd get without a filter at your aperture and ISO. Set the shutter speed you want for your shot. The calculator counts the stops between them and recommends the filter — rounding up to a real filter strength, because buying a filter one stop stronger than needed is safer than one stop weaker (you can always open the aperture or lower the ISO to compensate).
Worked example
Bright sun at f/8, ISO 100 (sunny 16 → EV 15): your base exposure without a filter is about 1/500 s. You want a 2-second exposure to smooth a waterfall: that's log₂(500×2) ≈ 10 stops → grab an ND1000, which gives exactly 2 s at 1/500 s base. Want 30 s instead? Add 4 more stops — an ND1000 plus a 2-stop ND4 stacked, or a single ND16000.
ND filter FAQ
How do I know which ND filter I need?
Meter the scene without a filter (or use the scene presets), decide the shutter time you want, then count the stops between them: every 3 stops ≈ 8× the exposure time. A 6-stop filter (ND64) is the all-rounder for daylight waterfalls; 10 stops (ND1000) for midday mist.
What does each ND filter do?
ND8 (3 stops) — gentle motion blur in shade. ND64 (6 stops) — moving water at dusk or in bright light. ND1000 (10 stops) — cotton-soft water at midday, empty streets. ND100000 (17 stops) — blackout-style exposures in full sun.
Should I buy a fixed ND or a variable ND?
Fixed filters give consistent colour and sharpness — best for landscape. Variable (VND) filters are convenient for video and run-and-gun, but can show X-shaped darkening at the wide end and are less colour-accurate.
Can I stack ND filters?
Yes — stops add: ND64 + ND8 = 9 stops. Watch for vignetting on wide lenses and a slight colour cast with cheap glass; a single filter is always optically better.