ND Filter Calculator
A neutral density (ND) filter is an optical filter that reduces the intensity of light passing through the lens by a fixed, spectrally flat factor, allowing photographers to use slower shutter speeds or wider apertures than would otherwise be possible in bright conditions. Each stop of ND doubles the required exposure time: a 3-stop ND8 filter turns a 1/100 s exposure into approximately 1/12.5 s, while a 10-stop ND1000 filter stretches the same 1/100 s to 10 seconds. ND filters are labelled in three overlapping ways: by stops (the most intuitive for photographers), by ND factor (the light-reduction multiplier), and by optical density (the base-10 logarithm of the multiplier, used in optics). This calculator converts between all three and shows the new required shutter speed in a readable format: fractions for sub-second exposures, decimal seconds for short exposures, and minutes and seconds for long exposures. Enter your base shutter speed without the filter and select your ND filter to see the result instantly. A reference table of all common ND filters is shown below the calculator.
New shutter speed: --
How to calculate new shutter speed with an ND filter
Each stop of ND filter doubles the exposure time needed to achieve the same exposure. The formula is straightforward: multiply your base shutter speed by the ND factor.
New shutter speed (s) = base shutter speed (s) × ND factor
Worked example
Base shutter speed 1/100 s (0.01 s), ND1000 filter (10 stops, factor 1000):
- New shutter speed = 0.01 × 1,000 = 10 seconds
- This is displayed as: 10.00 s
Base shutter speed 1/250 s (0.004 s), ND64 filter (6 stops, factor 64):
- New shutter speed = 0.004 × 64 = 0.256 seconds
- This is displayed as: 1/4 s (rounded to nearest common fraction)
ND filter reference table: stops, factors and optical density
The table below shows all common ND filters and the relationship between stops, ND factor (the light-reduction multiplier) and optical density (OD). Optical density is the base-10 logarithm of the ND factor: OD = log10(ND factor). Note that ND1000 is 10 stops because log2(1000) is approximately 9.97, which manufacturers round to 10.
| Stops | ND factor | Optical density (OD) | Common filter name | Shutter multiplier |
|---|---|---|---|---|
| 1 | 2 | 0.3 | ND2 | ×2 |
| 2 | 4 | 0.6 | ND4 | ×4 |
| 3 | 8 | 0.9 | ND8 | ×8 |
| 4 | 16 | 1.2 | ND16 | ×16 |
| 5 | 32 | 1.5 | ND32 | ×32 |
| 6 | 64 | 1.8 | ND64 | ×64 |
| 10 | 1,000 | 3.0 | ND1000 | ×1,000 |
| 15 | 32,768 | 4.5 | ND32000 | ×32,768 |
When to use ND filters
ND filters are most commonly used in three situations. First, for long-exposure landscape photography: smoothing waterfalls, blurring moving clouds, or creating silky-smooth sea surfaces in daylight where a slow shutter would otherwise massively overexpose the image. A 6-stop to 10-stop filter is typical for this use.
Second, for wide-aperture shooting in bright light: shooting portraits at f/1.4 in bright sun without overexposing, or using a shallow depth of field on a video camera that must maintain a fixed shutter speed (usually twice the frame rate, per the 180-degree shutter rule). A 3-stop to 6-stop filter is often sufficient here.
Third, for very long exposures: removing moving subjects from an image (pedestrians, cars), recording the arc of the sun across the sky, or creating abstract motion effects in architecture and cityscapes. Exposures of several minutes require 10 to 15 stops of ND.
When stacking ND filters, add the stops together. An ND8 (3 stops) stacked with an ND64 (6 stops) gives 9 stops total, with a combined multiplier of 8 × 64 = 512.
ND filter calculator: frequently asked questions
What is an ND filter?
A neutral density (ND) filter is a piece of optical glass or resin that reduces the amount of light entering the lens by a fixed factor, without affecting colour or contrast. Photographers use ND filters to allow slower shutter speeds in bright light, creating motion blur in waterfalls, clouds or traffic, or to shoot at wide apertures in daylight without overexposing the image.
How many stops is an ND1000 filter?
An ND1000 filter reduces light by a factor of 1,000, which corresponds to approximately 10 stops. Because stops are on a base-2 logarithmic scale, the exact stop count is log2(1000), which is approximately 9.97, rounded to 10 stops in practice. Manufacturers sometimes label the same filter as ND3.0 (referring to the optical density, which is the base-10 logarithm of the transmission factor).
What is optical density (OD)?
Optical density is a base-10 logarithmic measure of light transmission. An OD of 1.0 means the filter blocks 90% of light (passing 1/10), OD 2.0 blocks 99% (passing 1/100), and OD 3.0 blocks 99.9% (passing 1/1000). Photographers sometimes see filters labelled by OD rather than by stops or ND factor. The relationship is: stops = OD x (log2(10)), approximately 3.32 x OD.
When should I use a strong ND filter (10 or more stops)?
Strong ND filters (ND1000 / 10 stops or more) are used for very long exposures in bright conditions: smoothing out ocean waves over tens of seconds, recording cloud movement over minutes, or removing pedestrians from a busy street scene. They are also used in cinematography to allow very wide apertures in bright sunlight without overexposing. For these applications the shutter speed is typically measured in seconds, minutes or even hours.
Can I stack ND filters?
Yes. When two ND filters are stacked, their optical densities add together and their stop counts add together. For example, a 6-stop ND64 stacked with a 4-stop ND16 gives 10 stops (equivalent to ND1024, close to ND1000). The new shutter speed multiplier is the product of the two individual multipliers. However, stacking filters can introduce vignetting on wide-angle lenses and may slightly reduce image sharpness due to the additional glass elements.
Official sources
- Wikipedia: Neutral-density filter (stop, ND factor and optical density definitions).
- B&H Photo: Introduction to ND Filters.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology. General information only.