ND Filter Calculator
Free ND filter calculator: enter your base shutter speed and pick an ND filter to get the correct long-exposure shutter speed, with the stops and formula shown.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Show the formula & steps
How the ND Filter Calculator Works
A neutral density (ND) filter is a piece of dark glass that cuts the light reaching your sensor without changing colour. To keep the same exposure, you have to slow the shutter by the same number of stops the filter blocks. This calculator does that conversion: enter your base shutter speed (the reading without the filter) and choose your ND filter, and it returns the new shutter speed, the time in seconds, and the total light reduction.
The Formula
Every stop of light loss requires doubling the exposure time:
New shutter time = base time × 2^stops
The number of stops relates to the ND factor by stops = log₂(ND factor). So an ND8 filter (factor 8) blocks log₂(8) = 3 stops, and an ND1000 (factor ≈ 1024) blocks 10 stops.
| ND filter | Optical density | Stops | Time multiplier |
|---|---|---|---|
| ND2 | 0.3 | 1 | ×2 |
| ND4 | 0.6 | 2 | ×4 |
| ND8 | 0.9 | 3 | ×8 |
| ND16 | 1.2 | 4 | ×16 |
| ND64 | 1.8 | 6 | ×64 |
| ND1000 | 3.0 | 10 | ×1024 |
Worked Example
You meter a scene at 1/125 s and screw on a 10-stop ND1000 filter:
- Stops blocked = 10, so the multiplier = 2^10 = 1024
- New exposure = (1/125) × 1024 = 0.008 × 1024 = ≈ 8.2 seconds
Set your camera to an 8-second exposure (the nearest marked speed) in Bulb or Manual mode, keep the same aperture and ISO, and the brightness matches your original reading while the long exposure smooths moving water and clouds.
Tips for Sharp Long Exposures
- Use a sturdy tripod and a remote or 2-second timer to avoid shake.
- Focus and compose before fitting a strong ND, because the viewfinder goes dark.
- For exposures over 30 seconds, switch to Bulb mode and time it with the seconds figure above.
Frequently asked questions
What does an ND filter calculator do?+
It converts your base shutter speed into the longer exposure you need after attaching a neutral density filter. Because the filter blocks light, you must slow the shutter to keep the same brightness, and this tool does that math for you instantly.
How many stops is each ND filter?+
ND2 is 1 stop, ND4 is 2 stops, ND8 is 3 stops, ND16 is 4 stops, ND64 is 6 stops and ND1000 is 10 stops. Each stop doubles the required exposure time. The ND number is the light reduction factor, and stops equal the base-2 logarithm of that factor.
How do I calculate the new shutter speed?+
Multiply your base shutter speed by 2 raised to the number of stops the filter blocks. For a base of 1/125 s with a 10-stop ND1000 filter, 2^10 = 1024, so the new exposure is 1/125 × 1024 ≈ 8.2 seconds.
Should I change aperture or ISO too?+
No. The point of an ND filter is to keep your chosen aperture and ISO while lengthening the exposure. Lock in your aperture and ISO, meter without the filter, then apply the stop compensation to the shutter speed only.
Why use a neutral density filter at all?+
ND filters let you use slow shutter speeds in bright light to blur moving water, clouds and crowds, or to shoot wide open for shallow depth of field without overexposing. They reduce light evenly across all colours, so they do not shift your white balance.