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Shutter Speed Calculator

PhotographyExposure and Camera Settings
Metered exposure
New settings
Equivalent shutter speed —
Nearest 1/3-stop camera setting
—
Exact time (seconds)
—
Change from metered (stops)
—
Scene EV at ISO 100
—

To keep the same exposure, multiply the metered shutter time by (new f-number ÷ old f-number)² and by (old ISO ÷ new ISO). Metering f/16 at 1/100 s and ISO 100, then opening to f/8, gives 1/100 × (8 ÷ 16)² = 1/400 s. Each full stop of aperture or ISO halves or doubles the time.

About this tool

Photographers meter a scene at one setting and then want a different aperture for depth of field or a different ISO for noise. This calculator takes the metered aperture, shutter speed and ISO, plus the aperture and ISO you want, and returns the shutter speed that gives the same exposure. It also rounds to the nearest speed your camera offers in third stops, reports how many stops the time changed, and gives the scene's exposure value at ISO 100. It assumes the light stays constant and ignores reciprocity failure, so long film exposures beyond about one second need extra time from the film maker's chart.

How to use it

  1. Enter the metered exposure

    Type the aperture and ISO your meter used and pick its shutter speed from the list.

  2. Set the new aperture and ISO

    Enter the f-number and ISO you plan to shoot at.

  3. Read the shutter speed

    Use the nearest third-stop setting on the camera; the exact time and stop change sit beside it.

Examples

Sunny 16 at f/8

Metered aperture
16
Metered shutter speed
1/100 s
Metered ISO
100
New aperture
8
New ISO
100

Result Equivalent shutter speed: 1/400 s
Nearest 1/3-stop camera setting: 1/400 s
Exact time (seconds): 0.0025
Change from metered (stops): -2
Scene EV at ISO 100: 14.6

  1. Metered shutter = 1/100 s = 0.01 s
  2. Aperture factor = (8 ÷ 16)² = 0.25
  3. ISO factor = 100 ÷ 100 = 1
  4. New shutter = 0.01 × 0.25 × 1 = 0.0025 s (1/400 s)
  5. Change = log2(0.0025 ÷ 0.01) = -2 stops

Bright sun meters at f/16, 1/100 s, ISO 100. Opening to f/8 lets in four times the light, so the shutter must be four times shorter: 1/400 s.

f/8 to f/5.6, ISO 100 to 400

Metered aperture
8
Metered shutter speed
1/125 s
Metered ISO
100
New aperture
5.6
New ISO
400

Result Equivalent shutter speed: 1/1020 s
Nearest 1/3-stop camera setting: 1/1000 s
Exact time (seconds): 0.00098
Change from metered (stops): -3.03
Scene EV at ISO 100: 13.0

  1. Metered shutter = 1/125 s = 0.008 s
  2. Aperture factor = (5.6 ÷ 8)² = 0.49
  3. ISO factor = 100 ÷ 400 = 0.25
  4. New shutter = 0.008 × 0.49 × 0.25 = 0.00098 s (1/1020 s)
  5. Change = log2(0.00098 ÷ 0.008) = -3.03 stops

One stop from the aperture and two from ISO give about three stops, so 1/125 s becomes roughly 1/1000 s to freeze motion.

Low-light landscape on a tripod

Metered aperture
2.8
Metered shutter speed
1/60 s
Metered ISO
800
New aperture
11
New ISO
100

Result Equivalent shutter speed: 2.1 s
Nearest 1/3-stop camera setting: 2 s
Exact time (seconds): 2.057823
Change from metered (stops): 6.95
Scene EV at ISO 100: 5.9

  1. Metered shutter = 1/60 s = 0.016667 s
  2. Aperture factor = (11 ÷ 2.8)² = 15.4337
  3. ISO factor = 800 ÷ 100 = 8
  4. New shutter = 0.016667 × 15.4337 × 8 = 2.057823 s (2.1 s)
  5. Change = log2(2.057823 ÷ 0.016667) = 6.95 stops

Moving from f/2.8 and ISO 800 to f/11 and ISO 100 costs about seven stops, turning 1/60 s into roughly two seconds.

How it is calculated

t₂ = t₁ × (N₂ ÷ N₁)² × (S₁ ÷ S₂)

t₁, t₂
metered and new shutter time (s)
N₁, N₂
metered and new f-number
S₁, S₂
metered and new ISO speed

Light reaching the sensor is proportional to the shutter time and to 1 ÷ N², because the f-number is focal length divided by pupil diameter and the pupil area scales with its square. Sensitivity scales linearly with ISO. Holding exposure constant therefore gives the formula above. The stop change is log2(t₂ ÷ t₁), and the scene EV at ISO 100 is log2(N₁² ÷ t₁) − log2(S₁ ÷ 100), the APEX definition.

When not to use it

  • Long film exposures where reciprocity failure needs added time.
  • Scenes where the light is changing, such as a sunset, between metering and shooting.
  • Flash exposures, where the shutter speed hardly affects the flash part of the light.

Common mistakes

  • Treating f/5.6 to f/8 as half a stop; it is a full stop because area goes with the square.
  • Picking 1/125 when the meter said 1/250, which doubles the time and overexposes by a stop.
  • Forgetting that ND filters also change exposure and must be counted separately.

Frequently asked questions

Why does the f-number get squared?

The f-number is a ratio of focal length to aperture diameter. The light passed depends on the aperture area, which scales with the diameter squared. Going from f/8 to f/5.6 multiplies diameter by about 1.41 and area by about 2, which is one stop.

What is a stop?

A stop is a doubling or halving of light. Halving the shutter time, doubling the ISO or moving one full f-number step (f/4 to f/5.6) each change exposure by one stop. A negative stop change here means the new shutter time is shorter than the metered one.

Why is the exact speed different from the nearest camera setting?

Cameras offer speeds in third-stop steps such as 1/800, 1/1000 and 1/1250. The formula gives a continuous value like 1/1020 s, so the tool also picks the listed speed closest on a logarithmic scale. The difference is at most a sixth of a stop, which is well within normal exposure latitude.

What does scene EV at ISO 100 mean?

Exposure value combines aperture and shutter speed into one number: EV = log2(N² ÷ t). Normalised to ISO 100, it describes how bright the scene is. Bright sun is about EV 15, an overcast day about EV 12 and a lit interior about EV 7.

Does this work with the Sunny 16 rule?

Yes. Sunny 16 says that in bright sun f/16 at 1/ISO seconds gives a good exposure. Enter f/16, the nearest speed to 1/ISO and your ISO as the metered values, then set the aperture you want; the result is the Sunny 16 equivalent.

How do ND filters fit in?

An ND filter cuts light by a fixed number of stops, such as 3 stops for ND8 or 10 stops for ND1000. Work out the shutter speed here first, then multiply it by 2 raised to the filter's stop count.

Cite this tool

Using this tool in an assignment, article or report? Copy a citation, or a link for your website.

APA

Tools Directory Editorial Team. (2026, October 16). Shutter Speed Calculator. Tools Directory. Retrieved October 26, 2026, from https://tools.milunir.com/photography/exposure-and-camera-settings/shutter-speed-calculator/

MLA

Tools Directory Editorial Team. “Shutter Speed Calculator.” Tools Directory, 16 Oct. 2026, https://tools.milunir.com/photography/exposure-and-camera-settings/shutter-speed-calculator/. Accessed 26 Oct. 2026.

Chicago

Tools Directory Editorial Team. “Shutter Speed Calculator.” Tools Directory. Last modified October 16, 2026. Accessed October 26, 2026. https://tools.milunir.com/photography/exposure-and-camera-settings/shutter-speed-calculator/.

Link<a href="https://tools.milunir.com/photography/exposure-and-camera-settings/shutter-speed-calculator/">Shutter Speed Calculator – Tools Directory</a>