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Exposure Value Calculator

Calculate EV from aperture, shutter speed, and ISO.

The Exposure Value Calculator is a free photography calculator. Calculate EV from aperture, shutter speed, and ISO. Optimize your photographic settings with precise optical formulas for better results.
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What is Exposure Value (EV)?

Exposure Value (EV) is a single number that represents all combinations of aperture and shutter speed that produce the same exposure at ISO 100. An EV of 12 corresponds to f/8 at 1/125 second, or f/5.6 at 1/250 second, or f/11 at 1/60 second — all deliver identical brightness to the sensor.

Photographers use EV to compare light meter readings across different camera settings. A sunny beach might read EV 15, telling you that f/16 at 1/125 second (the Sunny 16 rule) will expose correctly. Indoor tungsten lighting might read EV 6, requiring f/2.8 at 1/30 second at ISO 100.

EV scales logarithmically: each +1 EV step doubles the light reaching the sensor, while -1 EV halves it. This matches how human vision perceives brightness changes and how camera exposure compensation works in one-stop increments.

Exposure Value Formulas with Worked Calculations

The standard EV formula at ISO 100 is:

EV = log₂(N² / t)

Where N is the f-number (aperture) and t is the exposure time (shutter speed in seconds).

Worked example: Calculate EV for f/5.6 at 1/250 second.

N² = 5.6² = 31.36

t = 1/250 = 0.004 seconds

N² / t = 31.36 / 0.004 = 7,840

EV = log₂(7,840) = ln(7,840) / ln(2) = 8.96 / 0.693 = 12.93 ≈ 13

Result: EV 13 — typical for overcast daylight or open shade.

To adjust for ISO other than 100:

EV₁₀₀ = EVᵢₛₒ - log₂(ISO / 100)

An exposure of f/4 at 1/60 second at ISO 400 gives EV 11 at ISO 400, which equals EV 9 at ISO 100 (two stops less).

How to Calculate Exposure Value: 6 Steps

  1. Identify your aperture: Your lens shows f/8. This is your N value. Standard full-stop apertures are f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22.
  2. Identify your shutter speed: Your camera displays 1/125 second. This is your t value. Convert fractions to decimals: 1/125 = 0.008 seconds.
  3. Square the f-number: 8² = 64. This represents the area of the aperture opening relative to focal length.
  4. Divide by exposure time: 64 / 0.008 = 8,000. This ratio determines total light captured.
  5. Calculate base-2 logarithm: log₂(8,000) = 12.97 ≈ 13. Use a calculator or EV table for this step.
  6. Adjust for ISO if needed: If shooting at ISO 200 instead of 100, subtract log₂(200/100) = 1. EV 13 at ISO 200 equals EV 12 at ISO 100.

5 Exposure Value Examples

Example 1 — Sunny 16 rule: Bright sunlight at f/16, 1/125 second, ISO 100. N² = 256, t = 0.008, N²/t = 32,000, EV = log₂(32,000) = 15. This matches the standard EV 15 for bright sun, confirming the Sunny 16 rule's accuracy.

Example 2 — Indoor portrait: Studio strobes at f/11, 1/200 second, ISO 100. N² = 121, t = 0.005, N²/t = 24,200, EV = log₂(24,200) = 14.57 ≈ 14.6. This high EV reflects the intense, controlled lighting of a professional studio setup.

Example 3 — Night photography: Cityscape at f/8, 4 seconds, ISO 400. N² = 64, t = 4, N²/t = 16, EV = log₂(16) = 4 at ISO 400. Convert to ISO 100: EV₁₀₀ = 4 - log₂(4) = 4 - 2 = 2. EV 2 matches typical urban night scenes.

Example 4 — Concert photography: Stage lighting at f/2.8, 1/100 second, ISO 1600. N² = 7.84, t = 0.01, N²/t = 784, EV = log₂(784) = 9.61 at ISO 1600. EV₁₀₀ = 9.61 - log₂(16) = 9.61 - 4 = 5.61 ≈ 5.6. This dim EV explains why concert photos often show noise.

Example 5 — Astrophotography: Milky Way at f/2.8, 25 seconds, ISO 3200. N² = 7.84, t = 25, N²/t = 0.3136, EV = log₂(0.3136) = -1.67 at ISO 3200. EV₁₀₀ = -1.67 - log₂(32) = -1.67 - 5 = -6.67. Negative EV values indicate extremely low light requiring long exposures.

4 Common EV Calculation Mistakes

  • Using shutter speed denominator instead of fraction: Entering 125 instead of 1/125 (0.008) produces EV = log₂(64 / 125) = -0.97 instead of the correct EV 13. Always convert shutter speeds to decimal seconds before calculating.
  • Forgetting ISO normalization: Comparing EV 14 at ISO 100 to EV 14 at ISO 3200 as equivalent. The ISO 3200 reading is actually EV 6.34 at ISO 100 — five stops darker. Always convert to ISO 100 baseline for meaningful comparisons.
  • Misreading f-stop scales: Assuming f/7 is a standard aperture. Full stops follow √2 progression: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22. Intermediate values like f/7.1 exist on modern cameras but weren't part of the original EV standard.
  • Ignoring reciprocal relationship: Thinking f/8 at 1/60 second differs from f/5.6 at 1/125 second. Both equal EV 12. Changing one setting requires opposite change in the other to maintain exposure — opening aperture by one stop means doubling shutter speed.

5 Tips for EV Calculations

  • Memorize common EV ranges: EV 15 = bright sun, EV 13 = overcast, EV 10 = open shade, EV 6 = indoor home lighting, EV 3 = dim restaurant, EV 0 = full moon. These benchmarks help you spot metering errors instantly.
  • Use EV for exposure compensation: If your meter reads EV 11 but you want one stop brighter for backlit subjects, target EV 10. This could mean f/5.6 at 1/60 second instead of f/8 at 1/60 second.
  • Check with Sunny 16: On a clear day, f/16 at 1/ISO second should expose correctly. At ISO 100, that's f/16 at 1/125 second (closest to 1/100). If your meter suggests f/8 at 1/500 second (also EV 15), both are valid.
  • Account for filter factors: A 3-stop ND filter reduces EV by 3. If meter reads EV 12, attach the filter and target EV 9 (or keep settings and accept three stops underexposure). Graduated NDs affect only part of the frame.
  • Verify with histogram: After calculating EV 10 for an indoor scene and shooting at f/4, 1/15 second, check the histogram. A centered peak confirms correct exposure. Histogram trumps calculated EV when scene reflectance differs from 18% gray.

4 Exposure Value FAQs

Professional incident meters measure EV 0 to EV 18 at ISO 100. Camera TTL meters typically span EV -2 to EV 20. EV 0 equals f/1.0 at 1 second — candlelight at close range. EV 18 equals f/1.0 at 1/8000 second — arctic snow in midnight sun.

Photography exposure is measured in stops, where each stop doubles or halves light. Base-2 logarithms directly represent stops: EV 12 to EV 13 is exactly one stop (2× light). Base-10 logs would require conversion factors that obscure the stop relationship photographers use.

Yes, but flash EV differs from ambient. Guide Number (GN) divided by distance gives the required f-number. For GN 40 (meters) at 5 meters: f/8. At 1/125 second sync speed, this equals EV 12. Flash EV applies only to the flash-lit portion of the exposure.

EV combines aperture and shutter speed into one number. ISO sits outside EV — it's sensor sensitivity, not light reaching the sensor. Think of EV as the light available, and ISO as how you amplify that light. Same EV works at any ISO with appropriate settings.

Written and reviewed by the CalcToWork editorial team. Last updated: 2026-04-29.

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Frequently Asked Questions

Professional incident meters measure EV 0 to EV 18 at ISO 100. Camera TTL meters typically span EV -2 to EV 20. EV 0 equals f/1.0 at 1 second — candlelight at close range. EV 18 equals f/1.0 at 1/8000 second — arctic snow in midnight sun.
Photography exposure is measured in stops, where each stop doubles or halves light. Base-2 logarithms directly represent stops: EV 12 to EV 13 is exactly one stop (2× light). Base-10 logs would require conversion factors that obscure the stop relationship photographers use.
Yes, but flash EV differs from ambient. Guide Number (GN) divided by distance gives the required f-number. For GN 40 (meters) at 5 meters: f/8. At 1/125 second sync speed, this equals EV 12. Flash EV applies only to the flash-lit portion of the exposure.
EV combines aperture and shutter speed into one number. ISO sits outside EV — it's sensor sensitivity, not light reaching the sensor. Think of EV as the light available, and ISO as how you amplify that light. Same EV works at any ISO with appropriate settings.