What is the Sunny 16 rule, and does it still work with digital cameras?
On a bright, sunny day with a clear, hard-edged shadow, set your aperture to f/16 and your shutter speed to roughly 1 over your ISO — at ISO 100, that's 1/100s (rounded to 1/125s on most cameras' available shutter speeds); at ISO 400, roughly 1/400s. That combination reliably produces a correct exposure in direct sunlight, and it still works exactly as well on a digital sensor as it did on film, because it's built on the physics of how much light direct sun actually delivers, not on any property specific to film.
Why This Specific Combination Works
Direct overhead sunlight delivers a remarkably consistent amount of light across most of the Earth's surface — consistent enough that a fixed exposure combination can serve as a reliable starting point without metering at all. The rule is really a memorized reference exposure value close to EV 14-15 at ISO 100 rather than a coincidence, and every other 'X 16' variant (Cloudy 11, Overcast 8, Sunset 4) follows the same shared-EV logic adjusted stop-for-stop as light drops.
Where It Still Genuinely Helps Today
Sunny 16 remains useful as a sanity check against your camera's meter, a fallback when a meter fails or gives an obviously wrong reading, and a fast manual starting point in bright, consistent outdoor light where fine-tuning from a known-good baseline is faster than metering from scratch. It's less useful in mixed, backlit or rapidly changing light, where the assumption of consistent direct sunlight breaks down and a real meter reading (or the histogram) is genuinely more reliable.
Work out the equivalent exposure at any aperture or ISO you actually want to shoot in the Exposure Triangle Solver, pre-filled with the classic Sunny 16 baseline.
Frequently Asked Questions
Does Sunny 16 work the same way in every country and season?
It's calibrated to strong, direct, high-angle sunlight, which is most reliable near midday and closer to the equator — early morning, late afternoon, high-latitude winter sun and any haze or thin cloud all reduce actual light levels below what the rule assumes, and the exposure needs adjusting accordingly.
Why does the shutter speed in Sunny 16 roughly match the ISO number?
It's a deliberate mnemonic simplification — the real relationship comes from EV math, but expressing the shutter speed as '1 over ISO' makes the rule easy to remember and apply without doing the underlying stop calculation in your head every time.