Calculate the exposure value (EV) of any camera setting and find equivalent aperture, shutter speed, and ISO combinations that keep the same exposure.
Your results will appear here.
Enter your values and press Calculate.
Enter your current aperture, shutter speed and ISO, then the new aperture and ISO you want to shoot with. The calculator finds the EV of your current settings and uses the reciprocity law to compute the exact shutter speed that keeps the same exposure when changing aperture or ISO, snapping the answer to the nearest real camera shutter speed and reporting the stop difference.
Equivalent exposure means different combinations of aperture, shutter speed and ISO that let the same total amount of light reach the sensor. This is the law of reciprocity in photography: a smaller aperture can be traded for a longer shutter speed, and a higher ISO can be traded for a faster shutter, with the final image brightness unchanged.
For example, f/2.8 at 1/1000 s and f/8 at 1/125 s are equivalent exposures. In the first, the wide aperture lets in lots of light for a very short time; in the second, the narrow aperture lets in less light for longer. Both give the same exposure value, so the photo comes out equally bright, but the depth of field and motion blur will differ. That creative difference is exactly why photographers learn equivalent exposure instead of memorizing one magic setting.
Every camera setting lives inside the exposure triangle: aperture, shutter speed and ISO. Aperture (the f-number) controls how wide the lens opens; a low f-number like f/1.8 lets in much more light than f/16. Shutter speed controls how long the sensor is exposed; 1/1000 s freezes motion while 1/30 s lets in more light but blurs movement. ISO controls how much the sensor signal is amplified; ISO 100 is clean and noise-free, while ISO 6400 brightens dark scenes at the cost of visible grain.
An aperture, shutter speed and ISO calculator ties all three together. Change one corner of the triangle and you must change another to keep the same exposure. Widen the aperture from f/8 to f/4 (two stops more light) and you can either shorten the shutter speed by two stops or drop the ISO by two stops. This calculator does that balancing math for you and shows the stop difference of every change.
Exposure value (EV) is a single number that describes how much light a setting captures. At ISO 100, the formula is:
EV = log2(N² / t)
where N is the f-number and t is the shutter speed in seconds. The calculator reports EV normalized to ISO 100, so settings shot at different ISOs stay directly comparable. Higher EV means a brighter scene or a more light-hungry setting.
To keep the same exposure when changing aperture and ISO, the new shutter speed is:
t2 = t1 × (N2/N1)² × (S1/S2)
where N1 and N2 are the old and new f-numbers, S1 and S2 are the old and new ISOs, and t1 is the original shutter speed. The stop change is log2((N2/N1)² × (S1/S2)); a negative result means you need a faster shutter, a positive result means a slower one.
Worked through by hand: from f/8, 1/250 s, ISO 100 to f/4, ISO 200. First, EV = log2(64 / 0.004) = log2(16000) = 13.97. Then t2 = 0.004 × (4/8)² × (100/200) = 0.004 × 0.25 × 0.5 = 0.0005 s, which is exactly 1/2000 s. The stop change is log2(0.125) = -3, so the shutter must move three stops faster. The calculator repeats this exact arithmetic for your own numbers.
An equivalent exposure settings table shows which combinations match each other. Every row below captures the same amount of light at ISO 100 (values are the nearest standard shutter speeds):
f/2.8, 1/1000 s = f/4, 1/500 s = f/5.6, 1/250 s = f/8, 1/125 s = f/11, 1/60 s = f/16, 1/30 s
Reading the table answers everyday questions instantly. If you are shooting at f/4 at 1/500 s and want the deeper focus of f/8, drop two stops of aperture and compensate with two stops of shutter: f/8 at 1/125 s. If you are at 1/30 s and f/11 but want the soft background of f/2.8, that is four stops wider, so 1/30 at f/11 equals about 1/500 at f/2.8, the nearest standard speed.
The calculator above turns any table lookup into a precise number, including the nearest real camera shutter setting and the exact stop difference, so you are never guessing between dial clicks.
Exposure value also describes scenes. Meter a scene and the camera reports its EV at ISO 100, which tells you how much light is available:
EV 0: dim night street, only street lamps EV 4: candlelit room EV 6: home interior in the evening EV 9: bright cloudy day outdoors EV 12: overcast day EV 13: bright but cloudy EV 14: hazy sunlight EV 15: full direct sun EV 16: bright sun on snow or sand
Handy anchor points at ISO 100: EV 0 is roughly f/1 at 1 s; EV 8 is f/16 at 1 s; EV 15, the classic sunny day, is f/16 at 1/125 s. The calculator reports the EV of your current settings, so you can compare them against this table and sanity check your meter: a bright beach at EV 9 probably means the meter is being fooled by the sky, not that the light changed.
1. Enter your current aperture as an f-number, for example 8 for f/8. 2. Pick your current shutter speed from the list, for example 1/250. 3. Pick your current ISO, for example 100. 4. Enter the new aperture you want to shoot at, for example 4 for f/4. 5. Pick the new ISO you want to use, for example 200. 6. Read the results: the exposure value of your current settings, the exact shutter speed that keeps the same exposure, the nearest standard shutter speed on a real camera dial, and the stop difference.
If the nearest standard shutter speed is not available on your camera, use the closest one and nudge ISO slightly to fine tune. Negative stop values mean the new settings are faster (less time needed); positive values mean they are slower.
Say you are shooting a portrait at f/4, 1/500 s, ISO 100, but you want everything sharp from the foreground flowers to the background trees, so you need f/8. Going from f/4 to f/8 closes the aperture by two full stops, which halves the light twice.
Apply the formula: t2 = (1/500) × (8/4)² × (100/100) = 0.002 × 4 = 0.008 s, which is exactly 1/125 s. The stop change is log2(4) = +2, so the shutter must slow by two stops. f/4 at 1/500 s to f/8 at 1/125 s is therefore an equivalent exposure: same brightness, much deeper focus.
The calculator gives you this answer directly: enter aperture 4, shutter 1/500, ISO 100, new aperture 8, new ISO 100, and it returns a required shutter speed of 0.008 s, nearest standard 1/125, with a +2 stop difference.
Photographers count light in stops because a stop is the most useful unit in the field: one stop is always a doubling or halving of light, no matter where you start. From f/5.6 to f/8 is one stop darker; from 1/125 s to 1/250 s is one stop darker; from ISO 200 to ISO 400 is one stop brighter.
The f-stop scale is built on the square root of 2, about 1.4, because the light passing through a lens depends on the AREA of the opening, and area grows with the square of the diameter. That is why the standard f-numbers run 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, each one stop apart. Shutter speeds and ISO use simple doubling sequences: 1/60, 1/125, 1/250, 1/500 and 100, 200, 400, 800.
Why do photographers use stops instead of exact numbers? Because exposure decisions are relative: knowing you need one stop more light tells you exactly what to do on any camera, in any light, without arithmetic. The calculator speaks the same language, reporting every change as a stop difference you can dial in directly.
The Sunny 16 rule is the classic starting point for outdoor exposure and a great way to check your meter. On a bright sunny day, set the aperture to f/16 and the shutter speed to the reciprocal of your ISO: at ISO 100 use 1/100 s (or the nearest 1/125 s), at ISO 400 use 1/400 s.
The Sunny 16 rule chart extends the idea to other weather:
Bright sun: f/16, shutter 1/ISO Hazy sun: f/11, shutter 1/ISO Cloudy bright: f/8, shutter 1/ISO Heavy overcast: f/5.6, shutter 1/ISO Open shade: f/4, shutter 1/ISO
Because these are equivalent exposures, you can trade them freely: sunny-day f/16 at 1/125 s equals f/8 at 1/500 s, which equals f/4 at 1/2000 s. Feed any of these starting points into the calculator above to translate them into the aperture or ISO you actually want to shoot with.
ISO is the third corner of the triangle and the easiest exposure adjustment in dark scenes, but it is not free light. Raising ISO amplifies the sensor signal, so ISO 3200 can make a dim room shootable where ISO 100 would need a tripod. The trade is digital noise: grain, reduced detail and weaker colors, especially in the shadows.
So can you change ISO instead of shutter speed to keep exposure? Yes, and it is often the smartest move. If you need f/2.8 for a blurry background and 1/500 s to freeze a running child, and the meter says the scene is one stop too dark, raising ISO from 100 to 200 fixes the exposure with zero change to depth of field or motion rendering. Modern cameras stay clean through ISO 1600 or 3200, so many photographers set a maximum auto ISO and let the camera handle it.
The calculator shows the brightness versus noise trade explicitly: enter your new ISO and it tells you exactly how much shutter speed you buy back, so you can decide whether the extra noise is worth it.
Equivalent exposure is a set of different aperture, shutter speed and ISO combinations that all capture the same total amount of light. Thanks to the law of reciprocity, closing the aperture by one stop and lengthening the shutter speed by one stop leaves the image equally bright, while changing the depth of field and motion blur for creative effect.
Exposure value is calculated with EV = log2(N² / t), where N is the f-number and t is the shutter speed in seconds. The calculator reports EV normalized to ISO 100 so different ISO settings stay comparable; for example f/8 at 1/250 s gives EV 13.97.
A good exposure value is simply the EV that matches the light in front of you. There is no universally best number: EV 15 suits bright sun, EV 12 suits overcast days, EV 6 suits indoor evenings and EV 0 suits night streets. Compare the EV reported by the calculator with the scene reference table to judge whether your settings fit the light.
Yes, ISO directly affects exposure: doubling the ISO from 100 to 200 adds exactly one stop of brightness, just like opening the aperture one stop or halving the shutter speed. That is why the equivalent exposure formula includes the ratio of old to new ISO, and why raising ISO is the quickest fix when you cannot change aperture or shutter speed.
Yes, and it is often the best choice. If you must keep a specific aperture for depth of field and a specific shutter speed to freeze or blur motion, changing ISO is the only remaining lever. The trade is noise: higher ISO adds grain, so weigh the brightness gain against image quality using the stop difference the calculator reports.
Photographers use stops because one stop always means a doubling or halving of light, wherever you start. It turns exposure into simple relative math: need one stop more light? Open the aperture one click, slow the shutter one click, or raise ISO one click. Every camera dial is marked in stops, so the unit matches the hardware.
Reciprocity is the principle that exposure depends on the total light collected, so aperture and shutter speed trade against each other: less light per instant times more time equals the same exposure. This is why f/2.8 at 1/1000 s and f/8 at 1/125 s are equivalent; the calculator applies this law to any two settings you enter.
Reciprocity failure happens with very long exposures, typically seconds or minutes, where film (and to a small extent digital sensors) responds less efficiently than the math predicts, so the image comes out darker than calculated. It matters for night photography, star trails and long-exposure landscapes: exposures beyond about 1 second may need extra time added. For the normal shutter speeds this calculator handles, reciprocity holds exactly.
Find percentages, percentage change and reverse percentages instantly.
Convert between metric and imperial length units.
Calculate speed, distance or time from the other two.
Estimate how many solar panels and what system size your home needs.