How do I work out the exposure time with an ND filter?

Multiply your shutter speed without the filter by the filter factor: 2 for each stop, so 64 for 6 stops, and 1,000 for an ND1000. 1/60 s with an ND1000 becomes about 17 seconds.

How many stops is an ND1000?

About 10 stops: 2 to the power of 10 is 1,024, close to its filter factor of 1,000. Its optical density is 3.0.

What if the exposure is longer than 30 seconds?

Many cameras stop timed exposures at 30 seconds. Switch to Bulb mode and time the exposure with a remote, an app or the camera's own bulb timer.

Should I meter and focus with the filter on?

With a strong filter, compose, focus and meter without it, switch to manual focus, then fit the filter and set the time from this calculator. On a camera with an optical viewfinder, cover the eyepiece during long exposures.

Free photo tools

ND filter calculator

Meter the scene without the filter, enter that shutter speed and the filter you are fitting, and get the exposure time to set.

Everything is worked out on your device: nothing is uploaded.

Work out the exposure time

Shutter speed without the filter Such as 1/125, 0.5 or 2 (seconds)

Filter

New exposure time: —
In seconds: —
Filter strength: —

How to use it

Without the filter, meter and note the shutter speed at your aperture and ISO.
Enter that speed, then choose the filter by its ND number or its stops.
Set the new time. Past 30 seconds, many cameras need Bulb mode and a remote or timer.

Questions

How do I work out the exposure time with an ND filter?: Multiply your shutter speed without the filter by the filter factor: 2 for each stop, so 64 for 6 stops, and 1,000 for an ND1000. 1/60 s with an ND1000 becomes about 17 seconds.
How many stops is an ND1000?: About 10 stops: 2 to the power of 10 is 1,024, close to its filter factor of 1,000. Its optical density is 3.0.
What if the exposure is longer than 30 seconds?: Many cameras stop timed exposures at 30 seconds. Switch to Bulb mode and time the exposure with a remote, an app or the camera's own bulb timer.
Should I meter and focus with the filter on?: With a strong filter, compose, focus and meter without it, switch to manual focus, then fit the filter and set the time from this calculator. On a camera with an optical viewfinder, cover the eyepiece during long exposures.