Exposure Calculator - EV From Aperture, ISO, Shutter

An exposure calculator turns the three camera controls that govern photographic exposure - aperture f-stop, shutter speed, and ISO sensitivity - into a single exposure value (EV) that matches the lighting in front of the lens. Photographers, videographers, and cinematographers use this tool to plan a shoot before they leave the house, to translate a lighting scene into one number, and to recover a missing camera setting when only two of the three are known.

• • Match Camera Settings To A Scene: Type in the f-stop, shutter speed, and ISO you plan to use and check that the resulting EV matches the lighting condition you are about to shoot.
• • Plan A Long Exposure: Pick the aperture and ISO you want for a Milky Way shot, set the target EV to -6, and read the shutter speed that gives the same exposure in seconds.
• • Translate A Recipe: Convert a recipe like f/8, 1/500 s, ISO 200 into a different combination that produces the same EV on a different camera.
• • Pick ISO For Indoor Light: Lock an aperture and shutter for indoor candlelight, then solve for the ISO that produces a printable image without visible noise.

Exposure value is the single number that ties the lighting of a scene to your camera's settings. When the EV of your settings matches the EV of the scene, the photograph is correctly exposed. The tool on this page keeps that comparison in one place so you do not have to memorise f-stop tables.

Practically, the page does two things. It scores a chosen combination of f-stop, shutter, and ISO with an EV, and it inverts the same equation to suggest one missing setting when you already know the EV you need.

When the same EV math has to hold across hundreds of frames at a fixed interval, Time Lapse Calculator plans the interval and total clip length using the exposure value you locked in here.

The calculator runs the standard EV formula used in photographic reference works: it squares the f-number, scales by a constant of 100, divides by the product of ISO and shutter time, and finally takes the base-2 logarithm of the result.

• aperture: Lens f-number; 8 means f/8, 2.8 means f/2.8.
• shutterSpeed: Time the shutter stays open, in seconds. 0.002 equals 1/500 s.
• iso: Sensor or film sensitivity. Doubling ISO doubles the response to light.
• targetEv: Optional exposure value used when solving for a single setting.

The exposure value is a logarithmic score, so a jump of one full EV either doubles or halves the amount of light reaching the sensor. Doubling the ISO adds one EV; halving the shutter speed adds one EV; widening the aperture by one f-stop also adds one EV.

When you ask the page to solve for one setting, it inverts the same equation. All three rearrangements - shutter = 100 * aperture^2 / (ISO * 2^EV), aperture = sqrt(ISO * t * 2^EV / 100), and ISO = 100 * aperture^2 / (t * 2^EV) - trace back to the original EV definition.

According to Wikipedia - Exposure Value, the exposure value is defined as EV = log2((100 * aperture^2) / (ISO * t))

Cambridge in Colour's Camera Exposure tutorial treats exposure as an interchangeable triangle, where the same total light is reached by trading a wider aperture, a longer shutter, or a higher ISO.

Long Milky Way and aurora shoots at EV -6 to EV -7 drain a battery faster than daylight work, so Battery Size Calculator helps you size the pack so the shutter, aperture, and ISO you set here hold for the whole night.

These four ideas underpin the formula and decide what each output of the calculator means in the field.

Treat aperture, shutter speed, and ISO as three dials on the same lever: any one of them can be turned up while another is turned down without changing the EV. Because EV is logarithmic, the step from f/2.8 to f/4 is the same as the step from 1/60 s to 1/120 s or from ISO 400 to ISO 800.

Exposure and composition travel together - locking the right EV lets you frame for the output aspect ratio you want, and CSS Aspect Ratio shows how width and height map to the standard photographic ratios like 3:2, 4:3, and 16:9.

Walk through these steps the first few times you use the tool. After two or three scenes the workflow becomes muscle memory.

1. 1 Pick What You Want To Solve: Open the Solve For menu. The default mode scores the three inputs against the lighting; the other three modes solve for shutter speed, aperture, or ISO at a target EV.
2. 2 Enter Your Three Settings: Type the aperture f-stop, the shutter speed in seconds, and the ISO. If your shutter is 1/500 s, type 0.002.
3. 3 Read The EV And Lighting Label: Look at the exposure value and the lighting condition label. If the label matches the scene, the camera settings are correctly exposed.
4. 4 Solve For A Missing Setting: Switch the Solve For menu to the variable you want to recover and enter a target EV from the lighting table in the Factors section.
5. 5 Iterate When The Lighting Changes: Repeat the workflow whenever the light shifts - golden hour to blue hour, indoors to outdoors.

You are shooting an outdoor portrait at f/5.6 and ISO 200 and want a shutter speed fast enough to freeze motion. Set Solve For to Shutter, leave aperture at 5.6, leave ISO at 200, and type a target EV of 13 to match an overcast afternoon. The page returns about 1/250 s.

After a shoot, a recipe like f/8, 1/500 s, ISO 200 produces 25 MB RAW frames that fill a card fast, and Data Storage Converter plans the card and backup capacity the run will need.

Putting the three exposure controls into one number saves real time during a shoot and prevents the most common mistakes that show up in image reviews.

• • Single-Number Lighting Score: Replace three knobs with one EV so you can tell at a glance whether your settings match the scene.
• • Solve For Any One Setting: Back out a missing shutter, aperture, or ISO when the lighting forces a change and only two settings are locked.
• • Plan A Long Exposure Before You Travel: Pick the aperture and ISO you want for a Milky Way shot, set the target EV, and read the shutter speed in seconds.
• • Build A Consistent Recipe Library: Record recipes like 'f/8, 1/500 s, ISO 200 = EV 14' so you can dial the same look across cameras that differ in sensor size.
• • Cross-Check Hand-Held Metering: Compare the camera's meter reading to the calculated EV; large disagreements usually mean a wrong ISO or switched aperture ring.

Used consistently, the calculator becomes a planning tool as much as a verification tool. Pairing the EV result with the lighting condition label also catches the most common beginner mistake: forgetting that ISO 100 and ISO 200 deliver the same EV only after a corresponding change in shutter or aperture.

When an extra lens or tripod might buy you one more usable stop of EV, Hobby Cost Calculator puts that gear decision on the same numeric scale as the exposure value the calculator returns.

EV is a clean theoretical score, but the real image depends on sensor size, lens transmission, and the dynamic range of the scene. These factors decide how close the calculator's number comes to the picture you actually take home.

• • The page assumes the standard logarithmic model and ignores lens transmission losses, so the displayed EV is an idealised score; treat it as the mid-tone exposure and bracket when the scene has high contrast.
• • Very high ISO values above ISO 12800 trade noise for sensitivity. The tool will happily return ISO 25600, but the resulting image will show visible noise on most cameras.
• • Bulb exposures longer than about 30 seconds suffer from reciprocity failure on film and read-noise on digital sensors.

Treat the calculated EV as the centre of an exposure envelope. Bracket one stop over and under when the lighting is tricky, and pair the EV with a histogram review after the first frame.

Wikipedia's APEX system article traces the EV formula back to the 1960 ASA PH2.5 standard, and lists the corresponding scene brightness from EV -6 starlight up through EV 16 bright snow.