Stops and density
Each stop halves the light, so you double the exposure time. The relationship is where n is the total number of stops. Filter density is often labeled in log₁₀ form: ND 0.3 ≈ 1 stop, ND 1.8 = 6 stops = ND64.
ND Filter Calculator
Calculate neutral density filter settings for long exposure photography.
ND Filter Calculator
ND filter strength
Total: 6 stops
Final shutter speed
1/2
Exact result
0.512 s
Total stops
6
Information hub
The math of stops
Each stop of ND filter halves the light reaching the sensor, so you must double the exposure time to compensate. The formula is Tfinal = Tbase × 2stops: your base shutter speed multiplied by 2 raised to the number of stops. Stack filters and their stops add (e.g. 6 stops + 3 stops = 9 stops total).
Density vs. stops
ND filters are labeled by density (ND factor) or by stops. Use this table to match your filter to the calculator.
| ND factor | Stops |
|---|---|
| ND2 | 1 |
| ND4 | 2 |
| ND8 | 3 |
| ND16 | 4 |
| ND32 | 5 |
| ND64 | 6 |
| ND128 | 7 |
| ND256 | 8 |
| ND1000 | 10 |
| ND1M | 20 |
The shutter speed scale
Cameras show shutter speeds as fractions (1/125, 1/500) for times under a second and as whole seconds with a quote (1", 15") for longer exposures—so the scale is easy to read at a glance. Your camera dial only has fixed steps (usually 1/3 stop). The calculator rounds the exact result to the nearest dial click so you can set the camera without mental math in the field.
Film & DSLR tips
Film: Very long exposures often need more time than the ND math suggests (reciprocity failure). Check your film's data sheet and add extra time if you're shooting multi-minute exposures. DSLRs: Cover the viewfinder during long exposures—light leaking in can cause flare or ruin the shot. Use the built-in curtain or a cover; mirrorless cameras don't have this issue.
ND filters and long exposure
How neutral density filters cut light by stops, how stacking adds up, and what to watch for with film and DSLRs.
Key ideas
Stacking
Stacking filters adds their stops (e.g. 6-stop + 3-stop = 9 stops). Use “Add filter” in the calculator to combine multiple filters and see the combined effect.
Reciprocity (film)
Film needs extra exposure time for very long shots; digital doesn’t. Check your film’s data sheet for long exposures.
Viewfinder leak
On DSLRs, cover the viewfinder during long exposures so stray light doesn’t reach the sensor. Mirrorless cameras avoid this.
ND Filter Calculator
Find the right shutter speed for long exposure and neutral density photography. Enter base exposure and filter strength (stops or ND density), stack multiple filters, and use red light mode in the field.
What this calculator does
This ND filter calculator gives you the final shutter speed after adding one or more neutral density filters. Enter your base shutter speed (presets from 1/64000 to 30 s or a custom value in seconds), then add filters by stop strength, from 1 stop (ND2) up to 20 stops (ND1M). You can stack multiple filters; stops add (e.g. 6-stop + 3-stop = 9 stops). The result is shown as a fraction for short times (e.g. 1/10 s) or as hours:minutes:seconds for long exposures. The tool rounds to the nearest 1/3-stop camera setting when useful. Red light mode and fullscreen are there for use in the field.
How the Math Works
Each stop of neutral density cuts the light reaching the sensor in half, so you must double the exposure time to compensate. The relationship is , where Tbase is your metered shutter speed without a filter and n is the total number of stops. Filter density in the ND labeling system uses base-10 logarithms: ND 0.3 equals 1 stop, ND 0.6 equals 2 stops, and ND 1.8 equals 6 stops (also called ND64, because 26 = 64). When stacking filters, add the stops: a 6-stop filter plus a 3-stop filter gives 9 stops total, and . As a worked example, if your metered exposure is 1/100 s and you attach a 6-stop ND filter, the adjusted shutter speed is 1/100 × 64 = 0.64 s, roughly 2/3 of a second.
How to Use This Calculator
Pick your base shutter speed from the dropdown (presets range from 1/64000 s to 30 s) or type a custom value in seconds. Click Add filter and select the filter strength in stops, presets include common values like 3 stops (ND8), 6 stops (ND64), and 10 stops (ND1024). To stack multiple filters, add another filter row; the calculator sums the stops automatically. The final shutter speed appears as a fraction for short exposures (e.g. 1/10 s) or in hours:minutes:seconds for long ones. The result is rounded to the nearest 1/3-stop camera setting when applicable. Use red light mode and fullscreen when shooting outdoors at night to preserve your night vision. All calculations are local, no internet connection needed in the field.
Stops vs. density
Filter strength is either in stops (each stop halves the light, so exposure time doubles) or optical density (ND 0.3 ≈ 1 stop, ND 1.8 = 6 stops = ND64). The math is with n = total stops. The calculator uses stops; the table in the info hub above maps common ND factors (ND2, ND4, … ND1000) to stop values so you can match your filter to the tool.
Reciprocity and viewfinder
On film, very long exposures often need more time than the ND formula suggests (reciprocity failure); digital sensors don’t have this, so the result is accurate for digital. For DSLRs, cover the viewfinder during long exposures so stray light doesn’t affect the image; mirrorless cameras don’t have this issue.
ND Filter Calculator FAQ
How do I use the ND filter calculator?
Pick your base shutter speed (e.g. 1/100s from the dropdown or enter a custom value in seconds). Add one or more filters and set each filter’s strength in stops (presets like 6 stops / ND64 are available). The tool shows the final shutter speed as a fraction for short times or as H:M:S for long exposures. Use red light mode and fullscreen when you’re out in the field.
Can I stack multiple ND filters?
Yes. Hit “Add filter” for each filter and choose its strength. Stops add: for example 6 stops plus 3 stops gives 9 stops total. The calculator multiplies your base exposure by 2 raised to the total number of stops to get the final shutter speed.
What is reciprocity failure?
On film, very long exposures often need more time than the simple ND math suggests, the emulsion becomes less sensitive over time. Digital sensors don’t have reciprocity failure, so the calculator’s result is accurate for digital. For film, add extra time according to your film’s data sheet.
Why cover the viewfinder on a DSLR for long exposures?
Light can leak through the viewfinder and reach the sensor, which can cause flare or ruin the shot. Use the built-in viewfinder curtain or a dedicated cover. Mirrorless cameras don’t have this problem.
Mathematical Reference Note
Calculation Logic: This tool uses standard mathematical algorithms. While we strive for accuracy, errors in logic or user input can result in incorrect data.
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