ND Filter Calculator
Use this ND filter calculator to work out the right shutter speed after fitting a neutral density filter. Meter the scene without the filter, enter that base shutter speed and the filter's strength in stops, and the calculator returns the long exposure you need — for silky water, streaking clouds, and motion blur in bright light.
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Calculate your long-exposure shutter speed
Enter values above and press Calculate to see your result.
Formula used
Each stop of ND doubles the exposure time. For N stops:
New shutter = Base shutter × 2^N
So a 10-stop filter multiplies the exposure by 2¹⁰ = 1024. A metered 1/125 s becomes about 8 seconds. ND filters are labelled in different ways — ND number (ND1000), optical density (3.0), or stops — which can be confusing; this tool works in stops.
Worked examples
10-stop, bright day. Base 1/125 s × 1024 ≈ 8 s — enough to blur moving water.
6-stop. Base 1/60 s × 64 ≈ 1 s.
Stacking filters. A 6-stop plus a 3-stop is 9 stops total; enter 9.
How to use this calculator
- Compose and meter the scene without the ND filter; note the shutter speed.
- Enter that base shutter speed and choose its unit (1/x or whole seconds).
- Enter the filter strength in stops.
- Press Calculate for the corrected shutter speed.
- Use a tripod; if the result is over 30 s, switch to Bulb mode with a remote.
ND filter strength reference
| ND number | Optical density | Stops | Light reduction |
|---|---|---|---|
| ND2 | 0.3 | 1 | ½ |
| ND4 | 0.6 | 2 | ¼ |
| ND8 | 0.9 | 3 | 1/8 |
| ND64 | 1.8 | 6 | 1/64 |
| ND400 | 2.7 | 9 | 1/512 |
| ND1000 | 3.0 | 10 | 1/1024 |
Labels vary by brand; stops are the most reliable way to compare filters.
Who should use this calculator
Landscape, seascape and architecture photographers using ND filters for long exposures in daylight. It's also handy for video shooters working out how much ND they need to hit a target shutter angle in bright sun.
What each input means
- Base shutter — the correct exposure time before the filter goes on.
- Unit — fast shutters are written as 1/x; enter 125 for 1/125 s, or switch to whole seconds.
- Stops — the filter's strength; add stops together when stacking filters.
Practical long-exposure tips
- Focus and compose first, then fit a strong ND — autofocus often fails through a 10-stop.
- Use a tripod and remote or 2-second timer to avoid shake.
- Mind light leaks through the viewfinder on long exposures; cover it.
- Beyond 30 s, most cameras need Bulb mode and an external timer.
Limitations of this calculator
This gives the theoretical shutter speed. Real filters can vary slightly from their rated strength, very long exposures may need a small reciprocity adjustment on film, and you may choose to fine-tune for creative effect. Bracket if precise exposure is critical.
Frequently asked questions
How do I calculate shutter speed with an ND filter?
Multiply your base shutter speed by 2 raised to the number of stops. A 10-stop filter multiplies by 1024, turning 1/125 s into about 8 seconds.
How many stops is an ND1000 filter?
ND1000 reduces light by about 1000× — that's 10 stops (2¹⁰ = 1024).
Can I stack ND filters?
Yes. Add their stops together — a 6-stop plus a 3-stop equals 9 stops. Stacking can cause vignetting and slight colour cast.
What shutter speed blurs water?
Around 1–2 seconds smooths flowing water; several seconds or more gives a misty, glassy look. Use the calculator to reach that time in daylight.
What if my exposure is longer than 30 seconds?
Most cameras max out at 30 s in normal modes. Switch to Bulb and use a remote or intervalometer to time the exposure.