ND Filter Calculator

Calculate the new shutter speed after adding an ND filter — or work backwards to find the filter strength you need for a target exposure.

Inputs

Base shutter speed

ND filter

New shutter speed

1/4s

256 ms

Total stops

6 stops

Light reduced by

98.44%

Exposure timeline

015s30s

BaseWith ND

ND filter stop reference

Filter	Stops	Light reduction	1/250s becomes	Typical use
ND2	1 stop	50%	1/125s	Bright overcast days
ND4	2 stops	75%	1/60s	Video 180° rule
ND8	3 stops	87.5%	1/30s	Wide aperture in daylight
ND64	6 stops	98.4%	1/4s	Waterfalls, fast rivers
ND1000	10 stops	99.9%	4.1s	Seascapes, silky water
ND32000	15 stops	99.997%	2m 11s	Extreme long exposure

How to use this calculator

Forward mode — I have a filter, what exposure do I get?

01Meter the scene without any filter attached. Note the shutter speed your camera suggests for a correct exposure.
02Select that shutter speed from the Base shutter speed dropdown.
03Select your ND filter. The calculator instantly shows the new shutter speed you should use.
04To stack two filters, tap Stack a second filter and choose the second one. Their stop values add together and the result updates.
05The Exposure timeline bar shows where your new shutter falls. Amber warnings appear when a remote release is advisable; red when you need Bulb mode (over 30 seconds).

Reverse mode — I want a specific exposure, which filter do I need?

01Switch to Reverse using the toggle in the top-right corner of the calculator.
02Select your unfiltered base shutter speed — the exposure your camera meters without any filter.
03Enter your target exposure time in minutes and seconds. For example, 2 minutes 30 seconds for a long seascape shot.
04The calculator recommends the closest available ND filter and shows the actual exposure you will get with it. It also lists the three next-closest alternatives in case you need to adjust.

How ND filters work

An ND filter is sunglasses for your lens. It cuts the light coming in — without touching colour — so your camera has to keep the shutter open longer to get a correct exposure. That longer shutter is what turns a sharp, frozen waterfall into the silky flow you see in landscape photos.

What the number means

The number is how much light the filter blocks. ND64 blocks 64× the light; ND1000 blocks 1000×. Photographers usually talk about this in stops instead — each stop halves the light and doubles the shutter speed. So an ND64 (6 stops) turns a 1/250s base exposure into roughly 1/4s. An ND1000 (10 stops) turns that same shot into 4 seconds.

Stacking two filters

You can stack two ND filters on the same lens and their stops add together. An ND8 plus an ND64 gives you 9 stops combined — handy if you don't own every filter strength. Just be aware that stacking can cause vignetting on wide-angle lenses.

When you need Bulb mode

Most cameras stop at 30 seconds on the shutter speed dial. Go beyond that and you'll need Bulb mode, where the shutter stays open until you release the trigger. At that point a remote shutter release isn't optional — pressing the button by hand will shake the camera and ruin the shot. The calculator flags this for you when you get there.

How we calculate it

To find the new shutter speed after adding a filter:

t_{\text{new}} = t_{\text{base}} \times 2^{S}

where $t_{\text{new}}$ is your new shutter speed, $t_{\text{base}}$ is your original unfiltered shutter speed (both in seconds), and $S$ is the stop count of the filter — each stop doubles the exposure time.

To find how many stops you need for a target exposure:

S = \log_2\!\left(\frac{t_{\text{target}}}{t_{\text{base}}}\right)

where $t_{\text{target}}$ is the long exposure you want to achieve and $t_{\text{base}}$ is your metered shutter speed without any filter. The result gives you the exact stops needed — round to the nearest available filter.

For example: base shutter of 1/250s (0.004s) with an ND64 ( $S$ = 6 stops) gives $t_{\text{new}}$ = 0.004 × 2⁶ = 0.256s ≈ 1/4s.

FAQ

Does an ND filter affect white balance or colour?

A quality ND filter should be colour-neutral — hence the name. Cheaper filters often have a slight colour cast (commonly a cool blue-green tint). Shooting in RAW lets you correct this in post. Higher-end filters from brands like B+W, Haida, or Kase are more reliably neutral.

Should I focus before or after attaching the ND filter?

Always focus before attaching the filter, especially with a strong ND like an ND1000. Very dark filters make the viewfinder and autofocus nearly unusable. Once focused, switch to manual focus so the camera cannot accidentally refocus when you shoot.

What is a variable ND filter?

A variable ND (VND) consists of two polarising elements that rotate against each other to change the effective stop count — typically from 1 to 8 stops in a single filter. Convenient for run-and-gun shooting, but they can show an "X" pattern at maximum density and often have more colour shift than fixed-strength filters.

How do I correct exposure if my result is over or under?

Adjust ISO or aperture to compensate while keeping the same shutter speed. Raising ISO by one stop is equivalent to opening the aperture by one stop — both let in twice as much light, so you can halve the shutter speed to match.

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