What this Exposure Value Calculator does
This Exposure Value Calculator uses an aperture and shutter speed to calculate the exposure value represented by those camera settings. Enter the f-number and the exposure time in seconds, and the result shows the ratio of the squared f-number to the exposure time. For example, an aperture of f/4 and a shutter speed of 1/100 second correspond to 1,600 as this calculator's result.
There is an important distinction between that ratio and the conventional EV number. In photography, EV is usually expressed as a base-2 logarithm: EV = log₂(N² ÷ t), where N is the f-number and t is the exposure time in seconds. The supplied calculator formula uses the ratio N² ÷ t but cannot apply a logarithm with its supported arithmetic operations. Its result is therefore the value inside the logarithm, rather than the conventional logarithmic EV number. This makes the calculation transparent while allowing you to apply the base-2 logarithm separately if you need conventional EV.
The calculation also does not include ISO. It describes the relationship between aperture and shutter time for the entered settings. ISO affects the camera's sensitivity setting and the exposure needed for a given scene, so a complete exposure comparison should state ISO as well.
How to use the Exposure Value Calculator
- Enter the aperture as an f-number, such as 2.8, 4, or 8. Do not enter the letter f or a slash.
- Enter the shutter duration in seconds. For a 1/100-second exposure, enter 0.01. For 1/500 second, enter 0.002.
- Read the Exposure Value (ratio) result. It is calculated from the entered values and displayed to two decimal places.
Keep units consistent. The shutter input is seconds, not a denominator such as 100 for 1/100 second. A longer exposure time produces a smaller ratio when aperture remains fixed. A larger f-number produces a larger ratio when shutter time remains fixed.
Worked example: At f/4 and 1/100 second, the formula is 4² ÷ 0.01 = 16 ÷ 0.01 = 1,600. The calculator displays 1600.00. The conventional EV number for the same settings is log₂(1,600), approximately 10.64. That logarithm is outside the calculator's formula and is included here only to clarify the distinction.
How the Exposure Value Calculator formula works
The formula squares the aperture f-number, then divides by the shutter duration in seconds. Squaring the f-number is part of the standard relationship used in exposure calculations. The result is a ratio that can serve as the argument to the conventional EV logarithm.
In the conventional expression, N² ÷ t is converted to an EV number by taking its base-2 logarithm. Each increase of one conventional EV stop represents a doubling of this ratio. Since this calculator returns the ratio itself, compare ratios with care: a ratio twice as large corresponds to one EV higher under the same convention.
The distinction matters because a large ratio such as 1,600 is not a conventional EV number of 1,600. The two values use different scales. The calculator labels its output “Exposure Value (ratio)” to make clear which one it reports.
- Aperture: enter the f-number shown by the camera or lens.
- Shutter time: convert a fractional shutter speed to seconds before entering it.
- ISO: this calculator does not use ISO, so note it separately when documenting or comparing a photograph.
Use cases for the Exposure Value Calculator
This calculation can help photographers check how camera settings relate mathematically, organize notes from a shoot, or prepare a lesson about exposure. If you record aperture and shutter time for a series of images, the ratio gives you a consistent value to compare before taking the logarithm needed for conventional EV.
It can also help when discussing equivalent exposures. For example, photographers often adjust aperture and shutter duration in opposite directions to preserve exposure under steady lighting. The ratio can show whether those changes preserve the same N² ÷ t value. Keep ISO fixed for a straightforward comparison, because changing ISO changes the camera's sensitivity and the exposure interpretation.
For practical photography, the ratio alone does not predict whether an image will look correct. The scene's brightness, metering, lighting direction, lens transmission, camera calibration, and intended rendering can all affect the result. Treat this output as a calculation from two settings, not as a complete exposure recommendation.
Other factors to consider when calculating exposure
Shutter speeds are commonly written as fractions, while this calculator accepts decimal seconds. Convert carefully: 1/50 second is 0.02 seconds, while 1/200 second is 0.005 seconds. Entering 50 or 200 would describe a much longer duration and produce a misleading ratio.
Aperture markings are nominal f-numbers. The amount of light reaching the sensor can also depend on lens transmission, vignetting, filters, and equipment behavior. Those details are not modeled here. Similarly, the formula does not measure scene luminance or account for how a camera's meter interprets a scene.
For night photography, motion, or changing light, the same numerical relationship may not express the creative result you want. A long shutter can blur moving subjects, while a small aperture can affect depth of field and diffraction. Use the calculation to understand the settings, then consider the image and shooting conditions.
Exposure Value Calculator FAQ
Does this calculate conventional EV?
It calculates N² ÷ t, the ratio used inside the conventional EV expression. Conventional EV applies a base-2 logarithm to that ratio. The calculator's supported formula does not include logarithms, so its labeled result is the ratio.
How do I enter a shutter speed of 1/125 second?
Convert the fraction to seconds: 1 divided by 125 is 0.008 seconds. Enter 0.008 as the shutter duration.
Does the result include ISO?
No. The formula uses aperture and shutter duration only. Record ISO separately when you need the full context for a photograph or exposure comparison.
Why does a smaller shutter-time value raise the result?
The formula divides by shutter duration. If aperture stays the same, dividing by a smaller positive duration gives a larger ratio. This is a mathematical relationship and does not by itself judge the image's exposure.
Can I use the result to choose camera settings?
You can use it to understand or compare the entered settings, but it does not measure a scene or account for subject motion, lighting, ISO, or creative intent. Check the camera meter and review the image in the conditions where you are shooting.