What Is an ND Filter Exposure Time Calculator?

A neutral density (ND) filter is a darkened piece of glass or resin that reduces the amount of light entering your lens without changing color. Adding one means your camera's meter reading is no longer accurate, so you need to work out the new, much longer exposure time yourself. This calculator does that math instantly from your base metered exposure and the strength of the ND filter you're using.

This is the same calculation printed on paper ND filter charts that many landscape and long-exposure photographers carry in their camera bag.

How to Read Your Results

New Exposure Time Needed

This is the shutter speed to dial in (or the Bulb-mode timer to set) once the ND filter is attached, to get the same overall exposure as your base metered reading.

Stops of Light Added

This shows how many stops of light the filter is blocking. Every stop doubles the exposure time needed — a 10-stop filter roughly turns a fast shutter speed into several seconds.

Filter Factor Used

This is the multiplier applied to your base exposure time. An ND1000 filter, for example, has a factor of 1000×, meaning the new exposure time is 1000 times longer than the base reading.

Real-World Example

Say you meter a waterfall scene at 1/125s without any filter, then attach a 10-stop ND1000 filter to smooth the water.

Setting	Value
Base metered exposure	1/125s
ND filter	ND1000 (≈10 stops)
New exposure time	≈8 seconds

An 8-second exposure is long enough to blur moving water into a smooth, silky effect while everything else in the frame stays sharp on a tripod.

Tips for Long Exposure Photography

Always use a sturdy tripod for exposures longer than about 1/30s to avoid camera shake.
Focus and set your exposure before attaching a strong ND filter — autofocus and metering often can't see through very dark glass.
Use a remote shutter release or intervalometer for exposures over about 30 seconds, since most cameras cap their built-in timer there.
Check for color casts at very long exposure times — some budget ND filters shift color and may need correction in post-processing.

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Note: This calculator estimates exposure equivalence using standard ND filter stop math. It does not account for reciprocity failure on film, or sensor-specific noise behavior at very long digital exposures — always check a test shot before committing to a long session.

Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team

ND Filter Exposure Time Calculator

ND filter settings