What does f/2.8 at 1/125 second actually mean in terms of light? The Exposure Calculator turns your aperture, shutter speed, and ISO into one number called the exposure value, or EV. Photographers use that number to compare camera settings and to see what kind of scene they suit.
It works for students, hobbyists, and anyone learning the exposure triangle. You pick three settings from drop-down menus. The tool then shows two EV figures and a short scene label.
Table of Contents
- What the Calculator Does
- How to Use It, Step by Step
- The Exposure Value Formula
- Worked Example
- How to Read the Results
- Using EV in Practice
- Limitations and Assumptions
- FAQs About the Exposure Calculator
What the Calculator Does
The tool describes the settings you chose. It does not meter light or tell you if a photo will be too dark or too bright.
- Exposure Value (EV @ ISO 100): a number built from aperture and shutter speed only.
- Effective Exposure Index (EV @ ISO): the same number adjusted for the ISO you picked.
- Typical Scene Environment: a text label chosen from the first EV figure.
How to Use It, Step by Step
- Choose Aperture (f-stop) from f/1.4 to f/16. The sample is f/2.8.
- Choose Shutter Speed (seconds) from 1/1000s to 1 second. The sample is 1/125s.
- Choose Film / Sensor ISO Sensitivity from ISO 100 to ISO 6400. The sample is ISO 100.
- Press Calculate Exposure Value to refresh the results.
All three inputs are fixed lists, so you cannot type a custom value.
The Exposure Value Formula
EV is a base-2 logarithm. One step up means half as much light reaches the sensor. The tool squares the f-number and divides by the shutter time.
log2(f-number squared÷Shutter Seconds)=EV @ ISO 100
- EV at ISO 100 = log2(f² ÷ t), where t is the shutter time in seconds.
- EV at your ISO = EV at ISO 100 + log2(ISO ÷ 100).
- Both numbers are shown with one decimal.
- The scene label uses the EV at ISO 100 rounded to one decimal, the same number the card shows.
Worked Example
Tamika shoots indoors at f/2.8, 1/125 second, and ISO 100. The menu values are 2.8 and 0.008 seconds.
| Step | Calculation | Output |
|---|
| Squared f-number | 2.8 × 2.8 | 7.84 |
| Ratio to shutter | 7.84 ÷ 0.008 | 980 |
| EV at ISO 100 | log2(980) = 9.94 | EV 9.9 |
| EV at Your ISO | 9.94 + log2(100 ÷ 100) | EV 9.9 |
| Scene label | 9.9 is 9 or more, below 11 | Sunset / Bright Artificial Studio |
Change only the ISO to 400 and the second figure becomes EV 11.9. Choose f/5.6, 1/60s, and ISO 200 for a different case. The first figure is EV 10.9 and the second is EV 11.9.
How to Read the Results
EV @ ISO 100 is the standard way to compare settings. Two combinations with the same EV let in the same amount of light. For example, f/8 at 1/250 and f/4 at 1/1000 both give 14.0.
EV @ ISO shifts the number up as ISO rises. A higher figure means the same light level can be met at that sensitivity.
Typical Scene Environment is a rough label tied to bands of EV. The results card is titled Exposure Value Results. Read the label as a hint, not a measurement.
Using EV in Practice
A well-known guide is the sunny 16 rule. In full sun, f/16 and a shutter near one over the ISO give a good starting point. The tool shows f/16 at 1/125 and ISO 100 as EV 15.0. Its scene label reads Bright Sun on Beach / Snow (Sunny 16).
Keep the EV the same while you trade settings. Opening the aperture one stop lets you raise the shutter speed one step. The depth of field calculator shows how aperture changes the zone that looks sharp.
Lens choice and sensor size also shape your look. See the focal length calculator and the camera crop factor calculator. For focus theory, the circle of confusion calculator adds detail.
If you plan prints, the camera megapixel calculator sizes them from pixels. Browse more in the everyday and lifestyle calculators hub.
Limitations and Assumptions
- The tool never reads a light meter. It cannot say whether your settings give a correct exposure.
- Despite the page title, it gives no reciprocal or equal-exposure settings list.
- F-numbers are the rounded values, such as 2.8 and 11. Real stops are 2.83 and 11.3, so the EV can be off by about 0.1 at most.
- Shutter values are rounded as well. The 1/60s choice uses 0.0166 seconds.
- Scene labels use fixed bands of the ISO 100 figure and are only rough guides. Changing ISO does not change the label.
- Exposure compensation, filters, and flash are not included.
FAQs About the Exposure Calculator
What is exposure value in photography?
It is a single number that links aperture and shutter speed to the light they admit. Higher EV means less light reaches the sensor.
Why do the two EV results match at ISO 100?
The second figure adds log2(ISO ÷ 100). At ISO 100 that term is zero.
Does the result tell me if my photo will be correct?
No. The tool describes your settings only. A light meter or your camera preview shows whether the scene is bright enough.
What EV is a sunny day?
Under the sunny 16 rule, full sun lands near EV 15 at ISO 100. Clouds and shade lower it.
Why does the sample show EV 9.9 and not 10?
The exact value is 9.94, which shows as 9.9. Rounding is done for display only.
Can I enter an aperture like f/3.5?
No. The menus list only the values shown. Choose the nearest option, or work the formula by hand.
This calculator gives general estimates only and is not professional advice. Reviewed for general accuracy by Prof. Dr. Khalil Mudassar, PhD.