Exposure Triangle Calculator
Equivalent exposures across aperture, shutter and ISO — and why a stop doubles the time but only multiplies the f-number by the square root of two.
Every row below is the same exposure, traded between the three settings. What changes is everything else: depth of field, motion blur and noise. "Equivalent" means equivalent in brightness only, which is the one thing the arithmetic can promise. Nothing is uploaded.
A stop doubles the light — but only multiplies the f-number by √2
In time and in ISO a stop is a factor of two. In f-number it is a factor of the square root of two, because the f-number is a diameter and the light comes through an area. So f/4 to f/2 is two stops, not one, and f/1 to f/64 is twelve. That single square root is the whole reason the aperture series looks arbitrary sitting next to the shutter series.
| One stop of… | From | To | Factor |
|---|---|---|---|
| Shutter time | 1/128 | 1/64 | ×2.0000 |
| ISO | 100.00 | 200.0000 | ×2.0000 |
| Aperture (f-number) | 4.00 | 2.8284 | ×0.7071 |
| Aperture area | 1.00 | 2.0000 | ×2.0000 |
Which is why every row here is the same picture as far as brightness goes — five stops of shutter traded against five stops of aperture, with an identical exposure value throughout.
| Aperture | Shutter | ISO | EV |
|---|---|---|---|
| f/8.00 | 1/31 | 100 | 10.966 |
| f/5.66 | 1/63 | 100 | 10.966 |
| f/4.00 | 1/125 | 100 | 10.966 |
| f/2.83 | 1/250 | 100 | 10.966 |
| f/2.00 | 1/500 | 100 | 10.966 |
| f/1.41 | 1/1000 | 100 | 10.966 |
And the numbers on your camera are rounded — in three blocks each
The even stops are exact, being whole powers of two. The odd ones are all rounded low, and not by the same amount: f/1.4, f/2.8 and f/5.6 are each exactly -1.005% out, f/11 and f/22 are -2.773% — nearly three times as far — and f/45 comes back to -0.563%, the closest of the lot. f/11 is really 11.3137. None of it matters: the worst case is under a twelfth of a stop.
| Marked | Exact | Error | In stops |
|---|---|---|---|
| f/1 | 1.0000 | 0.000% | 0.0000 |
| f/1.4 | 1.4142 | -1.005% | 0.0291 |
| f/2 | 2.0000 | -0.000% | 0.0000 |
| f/2.8 | 2.8284 | -1.005% | 0.0291 |
| f/4 | 4.0000 | -0.000% | 0.0000 |
| f/5.6 | 5.6569 | -1.005% | 0.0291 |
| f/8 | 8.0000 | -0.000% | 0.0000 |
| f/11 | 11.3137 | -2.773% | 0.0811 |
| f/16 | 16.0000 | -0.000% | 0.0000 |
| f/22 | 22.6274 | -2.773% | 0.0811 |
| f/32 | 32.0000 | -0.000% | 0.0000 |
| f/45 | 45.2548 | -0.563% | 0.0163 |
| f/64 | 64.0000 | -0.000% | 0.0000 |
The shutter dial splits into three blocks the same way — 2.400% long from 1/8000 to 1/125, 6.667% long from 1/60 to 1/15, and exact at 1/8 and slower where the marks already are powers of two. Inside a block the rounding cancels exactly: 1/125 to 1/250 is one stop to the last decimal place. It is only crossing between the blocks that costs you, and 1/125 to 1/60 is 1.0589 stops — six percent more light than the click suggests.
| Marked | Exact | Error | In stops |
|---|---|---|---|
| 1/8000 | 1/8192 | 2.400% | 0.0342 |
| 1/4000 | 1/4096 | 2.400% | 0.0342 |
| 1/2000 | 1/2048 | 2.400% | 0.0342 |
| 1/1000 | 1/1024 | 2.400% | 0.0342 |
| 1/500 | 1/512 | 2.400% | 0.0342 |
| 1/250 | 1/256 | 2.400% | 0.0342 |
| 1/125 | 1/128 | 2.400% | 0.0342 |
| 1/60 | 1/64 | 6.667% | 0.0931 |
| 1/30 | 1/32 | 6.667% | 0.0931 |
| 1/15 | 1/16 | 6.667% | 0.0931 |
| 1/8 | 1/8 | 0.000% | 0.0000 |
| 1/4 | 1/4 | 0.000% | 0.0000 |
| 1/2 | 1/2 | 0.000% | 0.0000 |
| 1s | 1s | 0.000% | 0.0000 |
How to use
- Enter your aperture, shutter speed and ISO.
- Read the exposure value and the nearest marked settings.
- Use the ladder to trade stops between aperture and shutter.
- Compare the marked numbers against the exact ones.
Frequently asked questions
What is a stop?
A doubling or halving of the light. In shutter time and in ISO that is a factor of two. In f-number it is a factor of the square root of two, because the f-number is a diameter and the light comes through an area.
Why is f/4 to f/2 two stops and not one?
Because halving the f-number quadruples the aperture AREA, and the area is what lets light in. Each factor of the square root of two in the f-number is one stop, so a factor of two is two stops.
Are the f-numbers on my lens exact?
No, and interestingly they are not all rounded the same way. f/1.4, f/2.8 and f/5.6 are each 1.005% below the true value, f/11 and f/22 are 2.773% below, and f/45 is 0.563% below. The even stops are exact.
Does that rounding matter?
Never to an exposure. The worst case across the whole series is under a twelfth of a stop, which no sensor or film could show you. It is worth knowing only because it explains why the numbers look so arbitrary.
Are the shutter speeds rounded too?
Yes, in three blocks. 1/8000 to 1/125 are all 2.400% long, 1/60 to 1/15 are 6.667% long, and 1/8 and slower are exact because those marks already are powers of two.
So is one click always one stop?
Inside a block, yes — exactly. 1/125 to 1/250 is one stop to the last decimal place, because both carry the same rounding and it cancels. Crossing between blocks it is not: 1/125 to 1/60 is 1.0589 stops, six percent more light than the click suggests.
What does equivalent exposure mean?
The same brightness from different settings — open up two stops and shorten the shutter by two and the picture is equally bright. What changes is everything else: depth of field, motion blur and noise all move even though the exposure does not.
Does this send anything anywhere?
No. Every figure is computed in your browser, and nothing is uploaded or stored.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.