What this Exposure Value (EV) Calculator does
The Exposure Value (EV) Calculator estimates an exposure value from three camera settings: aperture, shutter speed, and ISO. Its result is EV100, an exposure value normalized to ISO 100. This reference lets photographers compare exposures made at different ISO settings using a common scale.
The calculator uses the standard relationship EV = log2(N²/t), where N is the aperture f-number and t is shutter time in seconds. When ISO differs from 100, the EV100 equivalent is EV + log2(ISO/100). The calculator’s supported formula operations do not include logarithms, so it computes the underlying exposure ratio, N²/t × 100/ISO, rather than taking its base-two logarithm. The displayed number is therefore a linear ratio, not a conventional logarithmic EV value. A ratio of 100 corresponds to EV100 6.64 because log2(100) is about 6.64. Keep this distinction in mind when comparing the result with a camera meter or an EV chart.
This is a settings comparison aid. It does not judge whether a photograph is correctly exposed. The creative result also depends on the scene, the photographer’s intent, metering, lighting, and the camera’s measurement behavior.
How to use the Exposure Value (EV) Calculator
Enter the aperture as the f-number shown by the camera, the shutter time in seconds, and the ISO value. The defaults represent f/4, 1/100 second, and ISO 100. Check the units carefully, especially when converting a shutter speed displayed as a fraction.
- Aperture: Enter a value such as 2.8, 4, or 8. The input accepts f-numbers from 1 through 64.
- Shutter speed: Enter seconds, so 1/100 second is 0.01 and 1/500 second is 0.002. The permitted range is 0.0001 to 60 seconds.
- ISO: Use the numeric sensitivity setting, such as 100, 400, or 1600. The input range is 1 to 102,400.
For the default settings, the calculation is 4² / 0.01 × 100 / 100. That equals 1,600. The calculator displays 1,600.00 as the exposure ratio. Its EV100 equivalent is log2(1,600), or about 10.64 stops.
If a camera shows shutter speed as 1/100, divide 1 by 100 before entering the value. Entering 100 seconds would describe a much longer exposure and produce a very different result. Likewise, use the aperture number itself, not an estimate of the opening’s physical diameter.
How the Exposure Value (EV) formula works
The formula is aperture² ÷ shutter time × 100 ÷ ISO. Squaring the f-number reflects the relationship between aperture setting and light captured for a fixed scene. Dividing by shutter time accounts for how long the sensor receives light. The ISO adjustment expresses the result on an ISO 100 reference basis.
For a conventional exposure value, the logarithmic form is EV100 = log2(N²/t × 100/ISO). Each increase of one EV represents a factor of two in the exposure ratio. Because this calculator’s formula field supports multiplication, division, addition, subtraction, parentheses, and powers—but not logarithms—it returns the ratio inside that logarithm. It does not return a stop count. The title and result label identify the intended EV comparison, while the displayed numeric result should be interpreted according to the formula and this limitation.
A worked example uses f/8, 1/125 second, and ISO 200. Convert the shutter speed to 0.008 seconds. The ratio is 8² / 0.008 × 100 / 200, which equals 4,000. Its EV100 equivalent is log2(4,000), approximately 11.97. This example shows why the ratio can be useful for comparing settings while also differing numerically from EV expressed in stops.
Aperture and shutter speed can trade off while maintaining the same ratio. For example, opening the aperture by one stop and shortening the exposure time by one stop keeps N²/t approximately constant. ISO changes affect the ISO-normalized value, so comparisons should include the ISO setting rather than treating the exposure ratio as a complete record of the capture.
Use cases for the Exposure Value (EV) Calculator
Photographers can use the calculation to examine how a set of manual settings relates to another set. It is especially useful when reviewing exposure notes, practicing exposure reciprocity, or checking whether a change in ISO alters a normalized comparison.
- Compare two settings by calculating each ratio with the same units.
- Explore how aperture and shutter time compensate for each other.
- Document a camera setup alongside ISO for later reference.
- Learn why EV charts use a logarithmic scale while this result is a ratio.
For a direct comparison, make sure both calculations refer to the same scene and use the same convention. A ratio alone cannot tell whether highlights are clipped, shadows retain detail, or motion blur suits the photograph. It also cannot determine which exposure a photographer should choose.
Other factors to consider when calculating exposure
Camera settings describe only part of a photograph’s exposure. The scene brightness and light measurement method influence the exposure a camera recommends. A reflective meter can respond differently to a bright snow scene than to a dark subject, even if both are photographed with identical settings. The calculator has no scene or metering input, so it cannot model these conditions.
Lens transmission, filters, image stabilization, shutter calibration, and sensor response can also affect real-world results. The f-number is a geometric measure, while transmission is sometimes described by a T-stop in cinematography. Very long exposures may need additional consideration for reciprocity behavior or changing light. These factors are outside the formula.
Use the result as a mathematical comparison, then evaluate the image and camera meter for the intended outcome. Keep the aperture, shutter time, and ISO recorded together. That makes the calculation reproducible and avoids treating a single number as a universal judgment of image quality.
Frequently asked questions
Does this calculator return EV in stops?
No. Its supported arithmetic formula returns the exposure ratio before the base-two logarithm. Convert the ratio to conventional EV100 by taking log2 of the result. For instance, a ratio of 100 corresponds to about 6.64 EV100.
Why is the result normalized to ISO 100?
ISO 100 is a common reference for expressing exposure value. Adjusting by 100 divided by the entered ISO allows settings made at different ISO values to be compared on that reference basis.
How should I enter a fractional shutter speed?
Convert the fraction to seconds. Enter 0.01 for 1/100 second, 0.004 for 1/250 second, and 2 for a two-second exposure. The field expects seconds rather than a denominator such as 100 or 250.
Can a higher result tell me which photo is better exposed?
No. The ratio describes the entered settings under the formula. It does not account for scene brightness, metering, highlight detail, shadow detail, or creative intent, so it cannot rank photographs by exposure quality.
What does EV100 mean?
EV100 is the exposure value referenced to ISO 100. In its conventional form it is logarithmic and measured in stops. Here, the displayed result is the corresponding pre-logarithm ratio, so take its base-two logarithm to express it as conventional EV100.