Why does my camera underexpose snow?

Camera meters assume the scene averages to 18% middle grey. Snow is much brighter than middle grey, so the meter reduces exposure to bring it back to grey — resulting in underexposed, dingy-looking snow. Add +1 to +2 stops of exposure compensation to render snow as white.

When should I use spot metering?

Use spot metering when your subject is significantly brighter or darker than the background, such as a performer on a dark stage, a backlit portrait, or a bird against a bright sky. Spot metering reads only 2-5% of the frame, letting you meter precisely on your subject.

What is 18% grey and why does it matter?

All camera meters are calibrated to expose the scene as 18% grey (middle grey). This works for average scenes but fails for predominantly bright or dark subjects. Understanding this lets you predict when exposure compensation is needed.

How do I choose which parameter to compensate?

Adjust ISO if you want to keep aperture and shutter speed fixed (e.g. for consistent depth of field and motion blur). Adjust shutter speed if depth of field is more important. Adjust aperture if shutter speed must stay fixed (e.g. for motion blur control).

Metering Calculator — Exposure Compensation

Apply exposure compensation for tricky metering scenarios like snow, backlighting and dark subjects.

Aperture (f-number)

The f-number your meter suggests, e.g. 5.6

Shutter Speed (1/x)

The denominator only — enter 125 for 1/125s

ISO

The metered ISO, e.g. 100

Meter ModeRecords which mode you metered in — guidance only, it does not change the compensation maths below

Scene TypePick the scene the meter struggles with, or set a custom value

How We Calculate This

Camera meters assume every scene averages to 18% grey. This calculator shows how to compensate when that assumption fails:

Exposure Compensation

Each stop (1 EV) doubles or halves the light. To brighten by +C stops you need 2^C times more light, reached any one of three ways:

Corrected ISO = base ISO × 2^(compensation)

Corrected shutter = base shutter ÷ 2^(compensation) (longer exposure)

Corrected aperture = base aperture ÷ 2^(compensation ÷ 2) (smaller f-number = wider)

Positive compensation brightens the image (for snow, white subjects) — a higher ISO, a longer shutter or a wider aperture. Negative compensation darkens it (for black subjects, low-key scenes). Each option maintains the other two exposure parameters.

Grey-card reflectance

Camera meters are calibrated to 18% grey. If you meter off a card of a different reflectance, the suggested compensation shifts by log₂(reflectance ÷ 18%) — a brighter card (above 18%) needs a little more light, a darker one a little less. Leave it at 18% for standard metering.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.