By Ahsan Khowaja · Updated 27 October 2026
How to use the exposure calculator
- Pick a mode. Exposure value tells you how bright your current settings are. Equivalent exposure finds the shutter speed, aperture or ISO that keeps the same brightness after you change one of the others. ND filter turns a metered shutter speed into the longer one you need once the filter is on.
- Type the aperture as a plain f-number (8 for f/8, 2.8 for f/2.8) and the ISO as a number.
- Type the shutter speed the way the camera shows it:
1/125for a fraction of a second,2or30for whole seconds,0.5for half a second. - Read the headline result, then the "nearest marked" row. Cameras only offer click-stop values, so a computed 1/1020 s becomes 1/1000 s on the dial, and the row tells you how far off that is in stops.
This is a camera settings calculator for photographers. It does not cover screen-printing emulsion exposure or radiography exposure times, which use the same word for a different measurement.
How do you calculate exposure? The EV formula
Exposure value is one number that stands for every aperture and shutter speed combination letting the same amount of light through:
EV = log₂(N² ÷ t)
- N is the f-number (the aperture), so N² is 64 for f/8.
- t is the shutter time in seconds, so 1/125 s is 0.008.
- log₂ asks "how many times do I double 1 to reach this?". Each whole EV step is one stop, a doubling or halving of light.
Worked example: f/16 at 1/125 s. N² = 256, divided by 0.008 is 32,000, and log₂(32,000) = 14.97, which rounds to EV 15. That is the brightness the Sunny 16 rule describes: on a clear sunny day, f/16 at a shutter speed of 1/ISO gives a correct exposure, so f/16 at 1/100 s (or the nearest marked 1/125 s) at ISO 100.
The formula has no ISO in it, which surprises people. EV describes the camera settings; the scene brightness is EV at ISO 100, written EV₁₀₀. To get it, subtract the stops of sensitivity you added: EV₁₀₀ = EV − log₂(ISO ÷ 100). Our second example, f/2.8 at 1/60 s and ISO 800, is EV 8.9 on the dial but only EV 5.9 at ISO 100, the level of an ordinary room at night. The calculator shows both numbers so you can compare light levels between shots taken at different ISOs. The definition and the standard table of values are on Wikipedia's exposure value page.
EV chart: typical light levels at ISO 100
| EV₁₀₀ | Typical scene | f/16 shutter speed at ISO 100 |
|---|---|---|
| 16 | Bright sun on snow, sand or water | 1/250 s |
| 15 | Full or slightly hazy sun, hard shadows | 1/125 s |
| 14 | Hazy sun, soft shadows | 1/60 s |
| 13 | Bright cloudy day, no shadows | 1/30 s |
| 12 | Heavy overcast, or open shade in sun | 1/15 s |
| 9 to 11 | Sunset, dusk, deep shade | 1/2 s to 1/8 s |
| 7 to 8 | Floodlit sport, brightly lit shops, lit night streets | 1 to 2 s |
| 5 to 6 | Home interiors at night | 4 to 8 s |
| 0 to 3 | Candlelight, fairy lights | 30 s to 4 min |
These are rough guides, the kind printed on the exposure tables that came with film. Light meters disagree by a stop with each other on the same scene, and a backlit or very dark subject shifts the reading further. Use the chart to sanity-check a reading, not to replace one. The rightmost column is the Sunny 16 ladder: each step down is one stop, so the shutter time doubles.
Equivalent exposures: the exposure triangle in stops
Aperture, shutter speed and ISO each change the exposure in stops, and one stop of any of them is worth one stop of the others. That is the whole exposure triangle: if you open the aperture by two stops, you must shorten the shutter by two stops or drop the ISO by two stops (or one of each) to land on the same brightness.
- Aperture: stops = 2 × log₂(N₁ ÷ N₂). The f-number scale goes up by √2 per stop (1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22), so f/8 to f/2.8 is +3 stops, about 8× the light.
- Shutter speed: stops = log₂(t₂ ÷ t₁). Doubling the time is +1 stop. The marked speeds 1/125, 1/60, 1/30, 1/15 are rounded names; a few are not exact doubles, which is why computed results land a hair off a mark.
- ISO: stops = log₂(ISO₂ ÷ ISO₁). ISO 100 to 400 is +2 stops.
The equivalent exposure calculator solves one of the three for you: new shutter time t₂ = t₁ × (N₂ ÷ N₁)² × (ISO₁ ÷ ISO₂). Two worked examples:
- You metered f/8, 1/125 s, ISO 100 for a portrait and want f/2.8 for a blurred background. (2.8 ÷ 8)² = 0.1225, so t₂ = 0.008 × 0.1225 = 0.00098 s, shown as 1/1020 s; set 1/1000 s.
- You are at f/11, 1/60 s, ISO 100 and the shot is blurry from camera shake. Raising the ISO to 400 is +2 stops, so the shutter can be 4× shorter: 1/240 s, set 1/250 s.
Solving for the aperture uses a square root: N₂ = N₁ × √(t₂ ÷ t₁ × ISO₂ ÷ ISO₁). From f/4, 1/500 s, ISO 200 to 1/125 s at ISO 100 the net change is one stop too bright, so the lens closes one stop to f/5.7, which the dial calls f/5.6. Equivalent settings give the same brightness, not the same picture: a wider aperture means less depth of field, a longer shutter means more motion blur, and a higher ISO means more noise. Use the depth of field calculator to see what the aperture change does to focus.
ND filter exposure calculator for long exposures
A neutral density filter cuts the light by a fixed exposure factor, and the shutter time multiplies by that factor:
new shutter time = metered shutter time × filter factor, where factor = 2^stops.
| Filter | Optical density | Stops | Light passed | 1/125 s becomes | 1/15 s becomes |
|---|---|---|---|---|---|
| ND2 | 0.3 | 1 | 1/2 | 1/63 s (set 1/60) | 1/8 s |
| ND8 | 0.9 | 3 | 1/8 | 1/16 s (set 1/15) | 0.53 s |
| ND64 | 1.8 | 6 | 1/64 | 0.51 s | 4.3 s |
| ND400 | 2.6 | 8.6 | 1/400 | 3.2 s | 26.7 s |
| ND1000 | 3.0 | 10 (9.97) | 1/1000 | 8 s | 66.7 s |
| ND100000 | 5.0 | 16.6 | 1/100000 | 13 min 20 s | 1 h 51 min |
Filter makers label the same glass three ways: the factor (ND1000), the optical density (3.0, where density = log₁₀ of the factor) and the stops (10). A "10-stop" ND1000 actually passes 1/1000 of the light, which is 9.97 stops, close enough that the difference never shows in a photo. Meter without the filter, type that shutter speed into the long exposure calculator, pick the filter, and set the result. With two filters stacked, multiply the factors: ND8 on ND64 is 512×, or 9 stops.
Dense filters can fool autofocus and the meter, so focus and meter first, then screw the filter on and switch to manual. Very long exposures also warm the sensor, and a strong filter can add a colour cast that you fix in white balance later.
How to set exposure to 30 seconds or longer
Many cameras stop at 30 s in manual and shutter priority modes. For anything longer, switch to Bulb (the shutter stays open while the button is held, so use a remote or the self-timer) or to a built-in Time/Bulb timer or intervalometer if your model has one. Work backwards with the calculator: if you want 30 s of silky water in daylight metered at 1/30 s, you need a factor of 900, which is between ND400 (8.6 stops) and ND1000 (10 stops). An ND1000 gives 33 s, so close the aperture a third of a stop to land on exactly 30 s, or accept the extra 3 s.
What the calculator can't know
It uses the formulas above and nothing else, so it can't see your scene. The EV result is only as good as the meter reading you typed; exposure compensation you dialled in is already baked into that reading. Lens transmission is a little lower than the f-number suggests (cinema lenses use T-stops for this reason), filters are rarely exactly their nominal density, and reciprocity failure makes film need extra time on exposures beyond a few seconds, while digital sensors don't. If a result lands between marked values, round towards the side you care about: towards a faster shutter for sharpness, towards more exposure when shooting raw.
