About

NDFilterCalculator is a free, independent tool that converts a base shutter speed into the correct long-exposure shutter speed for a given neutral density (ND) filter, and includes a built-in countdown timer for the exposure itself. No account, nothing uploaded, no cost.

What it actually does

You pick (or type) your camera's base shutter speed — the speed your camera would use without any filter attached — and select an ND filter strength (or enter a raw stop value). The tool applies the standard doubling formula, new shutter speed = base shutter speed × 2^stops, and formats the result in human-readable minutes and seconds. It then offers a countdown timer, using the browser's Screen Wake Lock API where supported, so you can time the actual exposure without your phone's screen locking mid-shot.

Who this is for

Long-exposure and landscape photographers using ND filters (from a 3-stop ND8 up to 10-stop-plus "big stopper" style filters) who need a fast, reliable conversion instead of mental math or a paper chart, plus a practical way to time the resulting multi-minute exposure in the field.

What it is not

• It does not meter your scene or read your camera settings — you supply the base shutter speed, which you should determine with your camera's own meter (ideally before attaching a very dark filter, since metering through a strong ND can be unreliable).
• It doesn't account for reciprocity failure (a film-specific effect) or filter color cast — see the homepage FAQ for both.
• It is not affiliated with any ND filter manufacturer (Formatt-Hitech, Lee, NiSi, Breakthrough, Hoya, or otherwise) — the filter names in the dropdown are simply the common industry-standard stop equivalents.

How your data is handled

All calculations happen in your browser using plain JavaScript — nothing is uploaded to, or stored on, any server. See the privacy policy for full detail.

Contact

Questions or corrections: support@ndfiltercalculator.com

→ Calculate an exposure (free)