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One number for brightness
Photographers juggle three settings, aperture, shutter speed, and ISO, and it is easy to lose track of what combination gives the right brightness. Exposure value, or EV, collapses aperture and shutter speed into a single number, with an ISO adjustment that lets you compare settings across ISO values. Two settings with the same EV give the same brightness, so EV lets you trade aperture against shutter speed without changing exposure. This calculator converts your aperture, shutter speed, and ISO into EV and into EV at ISO 100, plus a rough scene match.
Scene matching makes the number useful. Bright sun on sand or snow sits near EV 15 at ISO 100, ordinary bright daylight near EV 14, cloudy daylight near EV 12, and indoor room light near EV 6 or 7. Night scenes fall to EV 0 or below. If your calculator result says EV100 15 but you are standing in a dim room, something is wrong with your settings, and the scene hint will flag it before you waste a shot. It is a sanity check, not a light meter replacement.
A worked example
Take f/8 at 1/125 second and ISO 100. The aperture squared is 64, divided by 1/125 gives 8000, and the base-2 logarithm of 8000 is about 12.97, so the EV is about 13.0 and the EV100 is the same, since ISO is already 100. That matches bright daylight with some cloud, which feels right for f/8 at 1/125: it is a classic daylight setting. Raise the ISO to 400 with the same aperture and shutter, and the EV100 drops to about 10.97, two stops lower, because the higher ISO brightens the image by two stops.
Now find an equivalent setting. F/5.6 at 1/250 second gives the same EV, because opening the aperture by one stop and halving the shutter time cancel out. That equivalence is the practical power of EV: you can choose the aperture you want for depth of field, then pick the shutter speed that keeps the same EV, or choose the shutter speed you want to freeze motion, then pick the aperture that matches. The calculator lets you test combinations quickly before you shoot.
The sunny 16 rule and EV
Low light shows the other end of the scale. An indoor room at EV 6 might need f/2 at 1/60 second and ISO 800, or f/2.8 at 1/30 and ISO 1600, both near the same EV100. The calculator helps you see those trade-offs: open the aperture for a faster shutter, raise the ISO for a faster shutter at the same aperture, or accept a slower shutter and use a tripod. Each choice has a cost, in depth of field, noise, or motion blur, and EV lets you compare the brightness side while you weigh those costs separately.
Using EV with a meter or a manual camera
Many older cameras and light meters report EV directly, and some photographers still set exposure by EV: meter the scene, read the EV, then choose any aperture and shutter combination with that EV. The calculator works in reverse for digital cameras: enter the combination you plan to use, read the EV, and compare it with the scene you are in. If the numbers disagree wildly, check your settings before shooting, because a one-stop error is easy to miss on a small screen in bright light.
Remember that EV describes brightness, not correctness for your subject. A backlit portrait and a sunlit landscape can share an EV yet need different exposure choices, because the meter reads an average while your subject may be far brighter or darker than that average. Use EV as a framework for equivalent settings and sanity checks, then use exposure compensation, spot metering, or a test shot to handle tricky light. The histogram on your camera is the final check, and it beats any number.
Remember that these are educational optical calculators. Exposure-value figures are estimates from the standard formulas, and real cameras, lenses, and meters vary slightly in transmission and calibration. Treat the calculator as a learning and planning tool, verify with a test shot in important situations, and let the histogram confirm the result.
Frequently asked questions
Why do two settings with the same EV look the same brightness? Because brightness depends on the total light reaching the sensor, and aperture times shutter time decides that total. Doubling the aperture area while halving the time keeps the total the same, so the image brightness matches, though depth of field and motion blur differ.
What is the difference between EV and EV100? EV describes your setting at your ISO, while EV100 converts it to the ISO 100 scale so settings at different ISOs can be compared. Scene brightness tables almost always use EV100, so use that number when matching a scene.
Can EV replace a light meter? No. EV converts settings you already chose, while a meter measures the scene to tell you which settings to choose. Use a meter, or your camera’s meter, to find the scene EV, then use this calculator to explore equivalent settings at that EV.
Use the calculator above with your aperture, shutter speed, and ISO, compare the EV100 with the scene hint, and explore equivalent combinations before you shoot. One number will not make you a better photographer, but understanding it will make your settings deliberate instead of accidental.