Free Exposure Calculator

Understanding Exposure Value in Photography

The Exposure Calculator — also known as a photography EV calculator, camera exposure calculator, or aperture‑shutter‑speed‑ISO calculator — is a free online tool that helps photographers determine the optimal combination of aperture, shutter speed, and ISO sensitivity for any lighting condition. By calculating the exposure value (EV), this tool ensures your images are neither underexposed nor overexposed.

What Is Exposure Value (EV)?

Exposure value is a numerical representation of scene brightness. Positive EV values (up to +15 or higher) indicate bright environments such as daylight, while negative values (down to –9 or below) correspond to very dim scenes like star fields or auroras. Matching your camera’s EV to the scene’s EV is essential for a correctly exposed photograph.

Key Factors That Influence Exposure

Three camera settings work together to determine the total exposure:

• Aperture (f‑stop): The opening that allows light into the camera. A lower f‑number (e.g., f/1.0) means a larger opening and more light; a higher f‑number (e.g., f/64) means a smaller opening and less light. Aperture also affects depth of field — the zone of acceptable sharpness.

• Shutter Speed: The length of time the sensor (or film) is exposed to light. Fast speeds (e.g., 1/2000 s) freeze motion but let in less light; slow speeds (e.g., 30 s) capture motion blur and allow more light.

• ISO Sensitivity: The sensor’s sensitivity to light. Low ISO (e.g., 100) yields cleaner images but requires more light; high ISO (e.g., 6400) brightens dark scenes but can introduce digital noise. The best practice is to use the lowest ISO possible and raise it only when needed.

These three parameters follow a reciprocal relationship: changing one requires adjusting another to maintain the same EV. This principle is at the heart of every exposure value calculator.

The Exposure Value Formula

The mathematical relationship between aperture, shutter speed, and ISO is expressed as:

$$\text{EV} = \log_{2}\left(\frac{N^{2} \times 100}{\text{ISO} \times t}\right)$$

where:

• $N$ is the aperture f‑number (e.g., 2.8 for f/2.8),
• $\text{ISO}$ is the ISO sensitivity (e.g., 200),
• $t$ is the shutter speed in seconds (e.g., 1/500 s = 0.002 s).

The logarithm base‑2 is used because each stop (halving or doubling of light) corresponds to a change of 1 EV. The constant 100 comes from the ISO 100 calibration standard.

Reference Table: EV for Common Lighting Conditions

The following table lists typical EV values for various real‑world situations. Use it as a quick reference to judge whether your current settings will produce a correct exposure.

EV	Lighting Condition
–7	Deep star field or Milky Way
–6	Night under starlight only; Aurora Borealis
–5	Night under crescent moon; Aurora Borealis
–4	Night under half moon; meteor shower (long exposure)
–3	Night under full moon, away from city lights
–2	Night snowscape under full moon, away from city lights
–1	Start/end of blue hour (outdoors); dim ambient indoor lighting
0	Dim artificial light indoors
1	Distant view of a lit skyline
2	Lightning (time exposure); total lunar eclipse
3	Fireworks (time exposure)
4	Candle‑lit close‑ups; Christmas lights; floodlit buildings; fountains; bright street lamps
5	Home interiors at night; fairs and amusement parks
6	Brightly lit home interiors at night; fairs and amusement parks
7	Bottom of rainforest canopy; brightly lit streets; floodlit sports areas; stage shows
8	Store windows; campfires; bonfires; ice shows; floodlit sports arenas; bright fluorescent interiors
9	Landscapes 10 min after sunset; city skylines; neon lights
10	Landscapes immediately after sunset; crescent moon through long lens
11	Sunsets; deep shade
12	Open shade; heavy overcast; half moon through long lens
13	Cloudy‑bright (no shadows); gibbous moon through long lens
14	Weak hazy sun; rainbows (soft shadows); full moon through long lens
15	Bright or hazy sun; clear sky (distinct shadows)
16	Bright daylight on sand or snow (distinct shadows)
17–19	Very bright artificial lighting
20+	Extremely bright artificial lighting; telescopic view of the sun

In camera metering, EV is typically rounded to the nearest whole number for simplicity.

How to Use the Exposure Calculator

This photography exposure tool is straightforward to operate. Simply input your aperture f‑stop, shutter speed, and ISO sensitivity; the calculator instantly returns the corresponding exposure value. If you have a target EV in mind, you can solve for any missing parameter by entering the known values.

For example, if you want to capture a starry night at EV –7, set your aperture to f/2.8 and ISO to 1600, then let the calculator determine the required shutter speed. Custom values (e.g., f/3.5 or 1/250 s) are supported by selecting the “custom” option for that field.

Worked Example

Suppose you are photographing a rainbow under a hazy sun using ISO 200 film. You set the aperture to f/8 and shutter speed to 1/500 s (0.002 s). Plugging these numbers into the formula:

$$\text{EV} = \log_{2}\left(\frac{8^{2} \times 100}{200 \times 0.002}\right) = \log_{2}\left(\frac{6400}{0.4}\right) \approx \log_{2}(16000) \approx 13.96$$

Rounding to the nearest whole number gives EV 14, which matches the table entry for rainbows under hazy sun. Therefore, the chosen settings are appropriate for the scene.

Additional Photography Calculators

Beyond exposure value calculations, photographers often need to estimate storage requirements. Tools such as image file size calculators and video file size calculators help plan memory card space for various formats, while time‑lapse calculators assist with interval settings. This exposure calculator, however, remains the essential starting point for mastering camera exposure.