Solving for shutter time
t = N² / (2EV100 × S/100)
At f/16, ISO 100, and EV100 15, the exact time is 1/128 second—very close to the familiar 1/125 camera setting.
Exposure Value Calculator
Camera settings
The field being calculated is hidden automatically.
Enter the f-number only, such as 2.8, 8, or 16.
Examples: 1/125, 0.008, or 2. Values without a slash are seconds.
ISO 100 is the EV100 reference sensitivity.
Enter the ISO 100-normalized light level or exposure target.
No input tracking: calculations and downloads are produced locally on this device.
Results
EV100
—
Enter valid settings to calculate.
Base EV (aperture + shutter)—
ISO-normalized EV100—
ISO adjustment from 100—
Exposure time—
EV arithmetic describes settings; it does not judge whether a photograph is correctly exposed.
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Equivalent aperture and shutter combinations
Each row keeps the same base EV and ISO. Closing the aperture by one stop requires twice as much shutter time.
| Aperture change | Aperture | Shutter speed | ISO | Base EV |
|---|---|---|---|---|
| 2 stops wider | — | — | — | — |
| 1 stop wider | — | — | — | — |
| Current | — | — | — | — |
| 1 stop narrower | — | — | — | — |
| 2 stops narrower | — | — | — | — |
How to use this exposure value calculator
- Choose a result. Calculate EV/EV100, shutter speed, aperture, or ISO.
- Enter the known values. Shutter speed accepts a fraction such as 1/125 or a time in seconds such as 0.008 or 2.
- Read both EV values. Base EV describes aperture and shutter only. EV100 also accounts for the entered ISO so different sensitivities can be compared on an ISO 100 basis.
- Check the practical match. When solving for a setting, the exact mathematical result and the nearest common camera setting are shown separately.
- Use the equivalence table. Trade aperture against shutter time while retaining the same base EV and ISO.
Exposure value formulas and assumptions
Exposure value is fundamentally an aperture-and-time number. Let N be the f-number, t be shutter time in seconds, and S be the ISO setting:
EV = log₂(N² / t)
EV100 = EV − log₂(S / 100)
The first formula means that f/1 for one second is EV 0. Moving one stop changes EV by exactly one. The second formula normalizes the settings to ISO 100: doubling ISO subtracts one from EV100 for the same aperture and shutter time.
Solving for aperture
N = √(t × 2EV100 × S/100)
The calculator reports the exact f-number and a nearby conventional full- or third-stop value when available.
Solving for ISO
S = 100 × N² / (t × 2EV100)
The ISO answer is a mathematical exposure index. Your camera may offer only rounded increments or a narrower range.
What the model excludes
This is exposure arithmetic, not a light meter. It does not model scene reflectance, flash duration, filters, bellows extension, lens transmission (T-stops), reciprocity failure, sensor response, dynamic range, or image processing.
EV versus EV100
Some references casually use “EV” for an ISO-adjusted light level. This calculator labels the two results explicitly. Base EV always means the aperture/shutter combination. EV100 is the ISO 100-normalized value used for cross-ISO comparison and many lighting-condition tables.
Representative check: the Sunny 16 relationship
At f/16 and 1/125 second, the base value is log₂(16² ÷ 0.008) ≈ EV 15. At ISO 100, EV and EV100 are equal. At ISO 400, keeping EV100 15 requires about 1/500 second at f/16 because the two-stop ISO increase is balanced by a two-stop faster shutter.
Further reading: Sony’s aperture, shutter speed, and ISO overview and the ISO 12232 digital-camera sensitivity standard overview.
Exposure value calculator FAQ
What is exposure value (EV)?
EV represents an aperture and shutter-time combination. All combinations with the same N²/t ratio have the same base EV, even if one uses a wider aperture and faster shutter.
What is EV100?
EV100 is an ISO 100-normalized value. It lets you compare settings made at different ISO values. The calculator subtracts log₂(ISO/100) from the base aperture/shutter EV.
Does a one-stop change equal one EV?
Yes. Doubling or halving the exposure is one stop, which changes the exposure value by one. Full-stop aperture changes use a factor of √2 because aperture affects exposure through the square of the f-number.
Is EV the same as exposure compensation?
No. EV describes exposure settings. Exposure compensation is a camera instruction that shifts an automatic meter’s chosen result brighter or darker, commonly expressed in the same stop-sized increments.
Can I enter a fractional shutter speed?
Yes. Enter 1/125, 1 / 2.5, or a decimal number of seconds. A bare number such as 2 means two seconds. Zero, negative, malformed, and excessively large values are rejected clearly.
Why is the calculated setting different from a camera dial?
The formula can produce values such as 1/128 second or f/5.657. Cameras usually round to standard full-, half-, or third-stop increments such as 1/125 and f/5.6. The exact and nearest common values are both shown.
Can EV tell me whether a scene is correctly exposed?
Not by itself. Correct exposure depends on measured light, subject reflectance, metering calibration, desired rendering, and the capture workflow. This calculator does not inspect the scene or image.
Should I enter an f-stop or T-stop?
The formula is defined with f-number. A T-stop includes measured lens transmission and may be more useful for matching cinema lenses, but inserting a T-stop here makes it an approximation rather than a strict f-number EV calculation.
Does this upload my camera settings?
No. Calculation, copying, and CSV generation run locally. The page does not send the aperture, shutter speed, ISO, or EV values you enter to a backend.