ND Filter Calculator
Meter the scene without a neutral density (ND) filter, then enter that shutter speed below. The calculator gives a starting exposure for one filter or a stack of two.
Meter the scene without a filter. Enter that shutter time, then choose how your filter is labeled.
Starting shutter time with filter
Calculating…
Calculation:
This is a starting exposure. Filter transmission, changing light, and long-exposure behavior can shift the final result; check a test frame and histogram.
How to calculate the shutter speed
Each stop doubles the exposure time. Multiply the unfiltered shutter time by 2 raised to the total number of stops. If your meter reads 1/125 second and you add 10 stops, the calculation is (1 ÷ 125) × 1,024 = 8.192 seconds.
A 6-stop filter makes a 1/60-second exposure about 1.067 seconds. Starting at 1/4 second with 10 stops produces 256 seconds, or 4 minutes 16 seconds. The numbers are estimates; take a test frame when you can.
Stops, filter factor and optical density
Filter labels use three related scales. Stops describe the exposure increase. A filter factor is the multiplier: 6 stops means 26, or 64 times the original shutter time. Optical density measures light reduction on a base-10 scale. To convert it to stops, divide the density by log10(2).
| Nominal strength | Exact factor from stops | Approximate optical density | 1/125 s becomes |
|---|---|---|---|
| 2 stops | 4× | 0.60 | 1/31.25 s |
| 3 stops | 8× | 0.90 | 1/15.625 s |
| 6 stops | 64× | 1.81 | 0.512 s |
| 10 stops | 1,024× | 3.01 | 8.192 s |
Labels are often rounded. For example, B+W lists its ND 3.0 filter as 10 stops and a 1,000× factor. An exact 10-stop multiplier is 1,024×, while an exact 1,000× factor is about 9.97 stops. Choose the label type printed on your filter rather than treating those rounded values as identical.
Choose a starting strength
First decide the shutter time you need for the effect. A 3-stop filter multiplies the metered time by eight; a 6-stop filter multiplies it by 64. A nominal 10-stop filter takes a 1/125-second meter reading into the neighborhood of eight seconds. The right strength depends on the light, aperture, ISO and the amount of motion you want to show.
When stacking filters, enter the second filter in stops. Their stop values add: 3 plus 6 stops gives 9 stops, so the shutter time is multiplied by 512. Check for vignetting and reflections with a stack, especially on a wide lens.
Why your final exposure may differ
The calculation assumes the light and camera settings stay the same after metering. In practice, the light may change while you fit the filter. A filter’s actual transmission may differ slightly from its printed label, and very long film exposures can require a reciprocity correction. Use the result as a first frame, check the histogram, then adjust.
Some cameras cannot time a long exposure with their ordinary shutter setting. Consult your camera manual for its timed-exposure limit and bulb or time mode. For shooting technique and filter choices, see our ND filter guide and long exposure photography guide.
Common questions
Does ND 1.0 mean ten stops?
No. ND 1.0 is an optical density value, equivalent to about 3.32 stops and a factor of 10. Ten stops corresponds to an optical density near 3.01.
What does ND1000 mean?
Usually it refers to a filter factor near 1,000×, close to 10 stops. Manufacturer naming varies, so check the specified factor or density for your exact filter.
Can I enter a fractional shutter speed?
Yes. Enter a fraction such as 1/125 or 1/4, or type a decimal number of seconds such as 0.5 or 2. The result is shown in seconds and, for longer exposures, minutes and hours.
Method: the calculator uses the exposure equations shown above. Filter-label examples were checked against the linked B+W manufacturer table on 30 September 2026. No filter was personally tested for this page.