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Free ND Filter Calculator
for
Cinematic Video
Enter your frame rate and current shutter speed – get your exact ND filter recommendation instantly. No math, no guesswork, no overexposed footage in the field.
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Check your camera's video settings — it will say 24fps, 25fps, etc.
Remove any filters first. Point at your scene, let it expose naturally, then enter the bottom number only (e.g. for 1/800 → enter 800).
The Fundamentals
What Is an ND Filter — and Why Does It Matter for Video?
Understanding why you need an ND filter is the difference between footage that looks cinematic and footage that looks like it was recorded on a security camera. Get it right before you hit record.
An ND (Neutral Density) filter is essentially a pair of sunglasses for your camera lens. It reduces the amount of light entering the sensor without altering colour, white balance, or contrast. This allows you to use a slower shutter speed in bright conditions – which is exactly what the 180° rule demands for cinematic video.
Without an ND filter in daylight, your camera is forced to use a very fast shutter speed – often 1/1000s or faster – to avoid overexposure. The problem is that fast shutters freeze motion completely between frames. The result is that choppy, stroboscopic look you see in amateur footage. Every small camera movement and every object in the frame loses its natural motion blur, making the footage feel unnatural and harsh to watch.
This is not a subtle difference. It is immediately noticeable to any viewer, even those with no knowledge of filmmaking. Films and television have trained audiences to expect a specific, natural-looking motion blur in video – and that blur only exists when you follow the 180° shutter rule.
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ND Filters Are Not Optional for Outdoor Video
Indoors or in low light, your camera can usually reach the correct shutter speed without any filter. But step outside on an average day and your camera will expose at 1/500s to 1/4000s or faster. The correct shutter at 25fps is 1/50s — that is anywhere from 10 to 80 times faster than where you need to be. An ND filter bridges that gap.
The number on the filter tells you its light-blocking power. ND8 blocks 3 stops of light. ND64 blocks 6 stops. ND1000 blocks approximately 10 stops. This calculator finds the closest standard filter to what your specific scene requires.
I personally find it easier to carry two variable ND filters rather than a set of fixed strengths. A variable ND lets you dial in the exact density for the light you’re in and the motion blur effect you want — no swapping, no guessing.
For my timelapse work I carry two that together cover the full range: the PolarPro Vario 2–5 Stop for overcast days and softer light, and the PolarPro Vario 6–9 Stop Mist Edition for bright sunshine and harsh midday conditions. Between the two, every situation is covered. Not sure which variable ND to buy? I break down every strength, the fixed vs variable trade-off, and my specific picks in the Best ND Filters for Timelapse: Strength Guide & Picks.
The 180° Rule
Why Your Shutter Speed Must
Be Double Your Frame Rate
The 180° shutter rule is one of the oldest and most consistently applied guidelines in filmmaking. It originates from the physical design of film cameras, where a rotating shutter disc with a 180° opening meant the shutter was open for exactly half of each frame cycle. Digital cameras have no mechanical shutter disc, but the visual principle it created has been used so universally that audiences now perceive it as natural.
The 180° rule states that your shutter speed should always be double your frame rate. Filming at 25fps? Your shutter should be 1/50s. At 30fps, 1/60s. This creates the natural motion blur your eye expects from cinema.
The rule works because at double the frame rate, each frame is exposed for exactly half the time between frames. This produces a specific ratio of sharp-to-blurred motion that human vision has come to associate with natural, fluid movement. Deviate significantly in either direction and the footage immediately looks wrong – either too sharp and stuttery, or too blurred and smeared. If you’re shooting on a drone, the same rule applies — we cover the exact ND filtersettings for each DJI model in our Manual Drone Camera Settings guide.
Shutter Too Fast
Motion looks choppy and unnatural. Each frame is too sharp. Footage has a stroboscopic, surveillance-camera feel. Common in beginner outdoor video.
Shutter Too Slow
Excessive blur makes footage look smeared and dreamlike. Fine for creative effect, but not suitable for standard cinematic video or client deliverables.
Shutter at 2× Frame Rate
Natural motion blur on every frame. Movement looks smooth and cinematic. This is the target the calculator aims for — every time.
Step-by-Step Guide
How to Use the ND Filter Calculator
From zero to correct filter in under two minutes. Here is exactly how to use each part of the tool in the field.
Select your frame rate
Choose the frame rate your camera is set to record in – not the playback rate, but the capture rate. For cinematic video intended for broad commercial or stock use, 24fps or 25fps are the most versatile choices. 30fps is standard for web delivery and US broadcast. If you are shooting slow motion, select 50fps, 60fps, or higher – the 180° rule still applies, and your target shutter will be much faster, meaning you will likely need a lighter filter or none at all.
Read your camera's live shutter speed without a filter
This is the most important step. Remove any filters already attached to the lens. Point your camera at the scene you are about to film and let it expose normally – either in auto exposure mode or by manually opening the aperture and adjusting ISO until the exposure looks correct. Now look at the shutter speed your camera is showing. It will appear as a fraction like 1/1600 or 1/500. Enter only the bottom number into the calculator – for 1/1600, enter 1600. This number tells the calculator how much light reduction is needed to reach your 180° target.
Read your recommended filter
The calculator immediately shows the closest standard ND filter that will bring your shutter down to the 180° target. It always rounds up to the next stronger filter to avoid underexposure — a slightly darker result is correctable in post; an overexposed shot is not. The plain-English description under the result tells you what conditions that filter is typically used for, so you can sanity-check the recommendation against your shooting situation.
Check the stops and target shutter readout
Below the filter recommendation you will see the target shutter speed and the number of stops of light reduction required. Stops are the standard unit photographers and videographers use to measure light – each stop either doubles or halves the light. ND32 is a 5-stop filter. ND64 is a 6-stop filter. If you own a variable ND filter, the calculator also shows you which range setting to use – a 1–5 stop variable ND or a 6–9 stop variable ND – so you always know where to position the ring.
Attach the filter and verify your exposure
Attach the recommended ND filter, switch your camera to manual shutter speed, and set it to the target shown by the calculator. Check that your exposure is correct – adjust aperture or ISO if needed, not the shutter speed. The shutter stays fixed at the 180° value. If the image is too dark after attaching the filter, open the aperture slightly or raise ISO. If it is still too bright, you may need a stronger filter – try the next step up.
Frequently Asked Questions
What is an ND filter calculator?
Do I need an ND filter for video?
What ND filter should I start with for general video?
What is the difference between ND32 and ND64?
What is a variable ND filter and should I use one?
Can I stack two ND filters together?
Does the 180° rule apply to slow motion video?
Also From AeroTimelapse
Complete Your Workflow
The ND filter calculator handles your exposure settings. For timelapse specifically, you also need the correct shooting interval, frame count, and storage estimate before you leave the house.
Get the Right Filter Before Every Shoot
Two minutes with the calculator before filming. Zero shots ruined by the wrong shutter speed.