Equivalent Shutter Speed Calculator
Photographers think about exposure in stops, where one stop is a doubling or halving of the light reaching the sensor. For shutter speed, opening up by a stop doubles the exposure time and lets in twice the light, while closing down by a stop halves it. This calculator converts a base shutter speed by a chosen number of stops so you can see the equivalent exposure time exactly. The rule is simple: multiply the base exposure time by 2 raised to the power of the stop change, with positive stops lengthening the exposure and negative stops shortening it. It is the everyday tool for balancing the exposure triangle: if you open the aperture by a stop you can shorten the shutter by a stop to keep the same brightness, and this gives you the matching time. Because standard camera shutter speeds are rounded for convenience, the exact factor-of-two result here may sit slightly off the nearest labelled setting, which is normal. Enter a base time as a decimal in seconds, set the stop change, and read the new shutter speed. Every figure here is computed deterministically from the reciprocity relationship shown below, with a worked example that reconciles exactly to the calculator.
A stop is a factor of two in light, so shutter time scales by powers of two: new time = base x 2^stops. A base of 1/250 s (0.004 s) opened by +2 stops becomes 0.016 s (about 1/63 s), four times longer.
Equivalent shutter speed formula
new time = base time x 2^stops
base time = starting exposure in seconds
stops = exposure change (+ lengthens, - shortens)
one stop = a factor of 2 in light
Each stop doubles or halves the light, so raising 2 to the power of the stop change scales the exposure time accordingly. A change of plus 2 stops multiplies the time by four.
Worked example
A base shutter speed of 1/250 second (0.004 s) is opened up by 2 stops.
- Exposure multiplier: 2^2 = 4.
- New time: 0.004 x 4 = 0.016 seconds.
- As a fraction: 0.016 seconds is 1 / 62.5, about 1/63 second.
The new shutter speed is 0.016 seconds (about 1/63 second). These are the calculator's default inputs, so the result above matches the widget exactly.
Stop change and exposure multiplier
| Stop change | Multiplier | Effect |
|---|---|---|
| -2 | 0.25x | Four times shorter |
| -1 | 0.50x | Half as long |
| +1 | 2.00x | Twice as long |
| +2 | 4.00x | Four times longer |
Measurement of time intervals: US National Institute of Standards and Technology.
Equivalent shutter speed calculator: frequently asked questions
What is an exposure stop?
A stop is a doubling or halving of the light reaching the sensor. For shutter speed, opening up by one stop doubles the exposure time (letting in twice the light), and closing down by one stop halves it. Stops are the common currency of exposure because aperture, shutter speed and ISO can all be adjusted in stops to keep the same brightness.
How do you change shutter speed by a number of stops?
Multiply the base exposure time by 2 raised to the power of the stop change. Positive stops lengthen the exposure (more light), negative stops shorten it (less light). For example, a base of 1/250 second adjusted by plus 2 stops becomes 1/250 times 4, which is about 1/62.5 second.
Why is this called reciprocity?
Shutter speeds are usually written as reciprocals, such as 1/250 second. Reciprocity in exposure refers to the trade-off between the variables that control light: a change in shutter speed by some stops can be balanced by an opposite change in aperture or ISO to keep the same exposure. This calculator handles the shutter-speed side of that relationship.
How do I keep the same exposure when changing aperture?
If you open the aperture by one stop, letting in twice the light, you can shorten the shutter time by one stop to compensate, and the exposure stays the same. Enter a negative stop change here to find the matching faster shutter speed, or a positive change if you closed the aperture down.
Are shutter speeds exactly one stop apart on a camera?
Standard full-stop shutter speeds, such as 1/60, 1/125, 1/250 and 1/500, are close to but not exactly one stop apart because the numbers are rounded for convenience. The exact relationship is a factor of two per stop. This calculator uses the exact factor of two, so its result may differ slightly from the nearest labelled camera setting.
Official sources
- Time and measurement standards: US National Institute of Standards and Technology (NIST). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.