ND Filter Calculator
Work out the new shutter speed after fitting a neutral density filter.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
About this calculator
An ND filter cuts light by a fixed number of stops, so the correct exposure is the unfiltered shutter speed multiplied by two to the power of the stop count. A 10-stop filter therefore turns 1/500 s into about 2 seconds — which is why long-exposure photography needs a tripod and a remote release rather than steady hands.
Worked example
calculated with the default values below
Shutter speed without filter 0.002 s · Filter strength 10 stops Shutter speed with filter 2.05 s · Exposure increase 1,024 × · Stops reduced 10.0 stops · Shutter speed reading 2 s · Original shutter speed reading 1/500 s
Method and assumptions
t₂ = t₁ × 2^s The factor 2^s doubles exposure per stop; display rule: ≥1 s shown rounded to 0.1 s, otherwise as 1/round(1/t) s. An ND filter cuts light by a fixed number of stops, so the correct exposure is the unfiltered shutter speed multiplied by two to the power of the stop count. A 10-stop filter therefore turns 1/500 s into about 2 seconds — which is why long-exposure photography needs a tripod and a remote release rather than steady hands. The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
Data sources
The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
Disclaimer
These calculators give general estimates. Sizing, pricing, availability and standards vary by brand, retailer and country, so treat the output as a starting point and confirm it against the seller's or authority's own figures.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
t₂ = t₁ × 2^s
- t₂
- new exposure time
- t₁
- base shutter time
- s
- ND filter strength, stops
The factor 2^s doubles exposure per stop; display rule: ≥1 s shown rounded to 0.1 s, otherwise as 1/round(1/t) s.
Frequently asked questions
How do I work out how many stops I need?
Divide the shutter speed you want by the one you can achieve without the filter, then take the base-two logarithm. To go from one hundred and twenty-fifth of a second to a full second is a hundred and twenty-five times longer, which is about seven stops. Each stop doubles the time, so counting doubles on your fingers is usually quicker than the logarithm.
Do cheap ND filters affect image quality?
Often noticeably, and in two ways. Very strong filters can leak infrared, which shifts dark synthetic fabrics and foliage towards a magenta or brown cast that is difficult to correct afterwards. Cheaper coatings also flare more and can show uneven density across the frame at high stop counts. This matters most for long exposures in bright light.
Which inputs and limits apply to ND Filter Calculator?
Use the units shown beside each field. These are form limits, not recommended settings. Shutter speed without filter: 0.00001–3,600 s; Filter strength: 1–20 stops t₂ = t₁ × 2^s The factor 2^s doubles exposure per stop; display rule: ≥1 s shown rounded to 0.1 s, otherwise as 1/round(1/t) s. An ND filter cuts light by a fixed number of stops, so the correct exposure is the unfiltered shutter speed multiplied by two to the power of the stop count. A 10-stop filter therefore turns 1/500 s into about 2 seconds — which is why long-exposure photography needs a tripod and a remote release rather than steady hands. The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
What is a complete worked example for Shutter speed without filter = 0.002 s; Filter strength = 10 stops?
Inputs: Shutter speed without filter = 0.002 s; Filter strength = 10 stops. Calculation: t₂ = t₁ × 2^s. Results: Shutter speed with filter = 2.05 s; Exposure increase = 1,024 ×; Stops reduced = 10.0 stops; Shutter speed reading = 2 s; Original shutter speed reading = 1/500 s.