Exposure Calculator

What it does

Uses the standard exposure-equivalence relationship between aperture, shutter speed, ISO and exposure value (EV) to solve for whichever one you don't know, given the other two plus a target EV.

What you'll need

• A target EV — if you already metered a scene and know its EV, enter that; otherwise use a known-good combination's EV as your target.
• The two exposure settings you already know (whichever two are left after picking what to solve for).

Steps

1. Choose which setting you want to solve for.
2. Enter your target EV and the other two known settings.
3. The result updates instantly as you type.

Reading the result

The result is the exact setting that reproduces your target EV given the other two values. Aperture and ISO are shown as their nearest values — your camera's actual dial moves in fixed stops (or thirds of a stop), so treat this as the precise target and round to your camera's nearest available setting.

Tips

• This is the same math behind "equivalent exposure" — e.g. if you open up one stop of aperture, this tells you exactly how much to speed up your shutter to compensate.
• EV values are conventionally given at ISO 100 in many references, but this calculator uses your entered ISO directly, so no separate ISO correction is needed.

What is exposure value (EV)?

Exposure value is a single number that stands in for a full combination of aperture, shutter speed and ISO — every combination of the three that lets the same amount of light reach the sensor shares the same EV. It compresses three dials into one comparable scale, which is what makes it possible to solve for any one setting once you fix the other two.

Why photographers use it

In practice you rarely want to change just one setting in isolation — you want to change one while keeping the exposure identical. Need a faster shutter to freeze a moving subject? Widening the aperture or raising the ISO by the matching amount keeps the same EV, so the shot stays correctly exposed instead of going dark. This calculator does that swap for you instead of you working the stops out by hand.

Which setting should you solve for?

Solve for shutter speed when the aperture is fixed by the depth of field you want and the ISO is fixed by your noise tolerance — this is the most common case. Solve for aperture when you have a fixed shutter speed (freezing motion, or matching a flash sync speed) and a fixed ISO. Solve for ISO last — it's the one to treat as the "remainder" once your creative aperture and shutter choices are locked in, since it's the setting with the most direct image-quality cost.

Common mistakes

• Pulling an EV number from an ISO-100 reference chart. and plugging it in here alongside a different ISO. This calculator's EV is relative to whatever ISO you enter, not the ISO-100 "light value" convention some exposure tables use — mixing the two conventions gives a wrong answer that looks plausible.
• Solving for aperture and getting a number your lens can't do. e.g. f/0.9 on a lens that only opens to f/1.8. The math is correct — your lens just can't reach it — so treat an out-of-range result as a sign to change a different variable instead, not a bug.
• Ignoring that ISO isn't a free variable. raising ISO to compensate for a faster shutter keeps the EV identical but adds sensor noise. The calculator will happily solve for ISO 12800 — whether that's an acceptable trade for your camera is a judgment call it doesn't make for you.
• Forgetting your camera's dials click in thirds of a stop. not continuous values — a solved result of f/6.3 is precise, but you'll actually dial in whatever your camera's nearest third-stop click is, which may read slightly differently on screen.
• Using this for flash exposure. the EV relationship here assumes continuous, metered light. Flash output doesn't work on the same aperture/shutter/ISO curve — use the Flash Power Matrix tool for that instead.

Example settings

FAQ

Does a higher EV mean a brighter or darker scene?

Brighter. A higher EV corresponds to more available light, which is why it demands less exposure — a smaller aperture, faster shutter, or lower ISO — to come out correctly exposed. A low EV (a dim room, night) needs more exposure to compensate.

Why doesn't my camera show the exact number this calculator gives me?

Camera dials move in fixed steps (usually thirds of a stop), while this calculator returns the precise mathematical target. Round to your camera's nearest available click — the difference is a fraction of a stop, well within normal exposure tolerance.

Can I use this to work out flash exposure?

No — this is for continuous, metered light. Flash exposure depends on the flash's guide number and distance to subject instead; use the Flash Power Matrix tool for that.

Where do I get my starting EV value?

Either from your camera's built-in meter (many cameras will display it, or you can back it into it from a known-good exposure), or from a standard reference like the Sunny 16 rule for outdoor daylight scenes.

Is this the same as "equivalent exposure" that photography guides talk about?

Yes — equivalent exposure is exactly this relationship. Any two settings combinations that land on the same EV produce the same overall brightness, just with different depth-of-field, motion-blur and noise trade-offs.