Exposure Value Calculator
Computes the Exposure Value (EV) at ISO 100 from aperture and shutter speed, giving a single number that represents the total light reaching the sensor. Use it to compare exposure settings or match lighting conditions across scenes.
Last updated: May 2026
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About this calculator
Exposure Value (EV) is a base-2 logarithmic scale that combines aperture and shutter speed into a single dimensionless number representing the total light admitted to the sensor. The formula is EV = log₂(N² / t), where N is the aperture f-number and t is the shutter speed in seconds. EV 0 is defined as f/1 at 1 second, and each increase of 1 EV represents half as much light (one full stop). At ISO 100, EV 15 corresponds to direct bright sunlight, EV 10 to overcast daylight, EV 5 to indoor lighting, and EV 0 to dim candlelight. Variables: N is the aperture and t is the shutter speed expressed in seconds — for 1/125 s enter 0.008, for 1 s enter 1, for 2 s enter 2. Edge cases: EV is calibrated to ISO 100; for other ISOs add log₂(ISO/100) — at ISO 400 the adjustment is +2 EV. The EV calculated from camera settings does not by itself say whether the exposure is correct; it must match the scene's measured luminance EV at the chosen ISO. Reciprocal pairs (e.g., f/8 at 1/125 s and f/5.6 at 1/250 s) yield the same EV but produce different DoF and motion-blur characteristics.
How to use
Example 1: f/8 aperture, 1/125 s shutter (enter 0.008 in the shutter field). Step 1: square aperture — 8² = 64. Step 2: divide by shutter — 64 / 0.008 = 8000. Step 3: take log base 2 — log₂(8000) = ln(8000) / ln(2) ≈ 8.987 / 0.693 ≈ 12.97 EV. Verify: EV 13 at ISO 100 corresponds to a bright overcast day or moderate shade in sunlight — consistent with sunny-16 rule (f/16, 1/100, ISO 100 = EV 15; opening 2 stops and slowing shutter 2 stops keeps EV similar to ambient). Example 2: f/16 aperture, 1 second shutter. Step 1: 16² = 256. Step 2: 256 / 1 = 256. Step 3: log₂(256) = 8 EV exactly. Verify: EV 8 corresponds to typical living-room indoor lighting at ISO 100 — about right for a candlelit scene with some lamplight.
Frequently asked questions
What does Exposure Value (EV) actually mean?
EV is a standardized number that describes the total luminous exposure of a camera setting independent of ISO. It combines aperture and shutter speed into one figure so photographers can quickly compare or communicate lighting conditions. An EV difference of 1 always represents a factor of 2 in exposure — exactly one stop. Because EV is logarithmic, the same EV can be achieved with many reciprocal aperture/shutter combinations, giving photographers creative control over depth of field and motion blur without changing the exposure. EV is also used in metering apps and gray-card readings to express scene brightness on a single, additive scale.
How do aperture and shutter speed combine to determine EV?
In the formula the aperture is squared before being divided by the shutter speed in seconds. Squaring is necessary because the area of the lens opening — and therefore the light admitted — scales with the square of the aperture diameter, which is inversely related to the f-number. Shutter speed appears in the denominator, so a faster shutter (smaller t) increases EV, meaning less light. Both controls have equal weight per stop: opening the aperture one stop or doubling the shutter speed each change EV by exactly 1. This is why the 'exposure triangle' treats aperture and shutter symmetrically when balancing exposure.
How is EV related to ISO and correct exposure?
The EV scale as calculated from aperture and shutter speed is calibrated to ISO 100. To find the 'correct' settings for a scene at a different ISO, add log₂(ISO/100) to the scene's measured luminance EV. Shooting at ISO 400 (two stops above ISO 100) effectively raises sensitivity by 2 EV, letting you use settings two stops 'darker' for the same brightness. Light meters and in-camera metering systems use this relationship to recommend aperture–shutter combinations matched to the measured scene EV at your selected ISO. Spot meters report scene luminance directly in EV at ISO 100 by convention.
What are common mistakes when calculating exposure value?
Entering '125' instead of '0.008' for a 1/125 second shutter speed produces nonsense results — the formula needs seconds, not the reciprocal. Forgetting the ISO offset when working at anything other than ISO 100 leads to confused exposure decisions; add log₂(ISO/100) explicitly. Using the actual aperture diameter in millimeters instead of the f-number gives unitless errors of several orders of magnitude. Confusing scene EV (a property of the lighting) with camera EV (a property of the settings) leads to mismatched exposures; the two must be equal for correct exposure. Finally, the EV scale is base 2 — using base 10 logs gives the wrong scaling entirely.
When should I NOT rely on EV calculations?
High-dynamic-range (HDR) scenes have a luminance range exceeding 10 EV between shadow and highlight, so a single exposure value cannot capture the whole scene — bracketing and merging is required instead. Flash photography uses guide-number math (intensity × distance) rather than ambient EV, because flash duration is fixed and aperture controls exposure. Cinematography uses Exposure Index (EI) and incident-light metering with specific cine-style adjustments rather than pure EV math. Astrophotography exposures sit far below EV 0 and require techniques like multi-frame stacking and dark-frame subtraction rather than a single EV setting. Mixed natural and artificial lighting often demands per-region exposure adjustments using masks rather than a global EV target.