# Aperture Area Calculator

URL: https://speedycalculator.com/calculators/physics/aperture-area/
Last updated: 2026-10-30

> The aperture area calculator finds a lens's entrance pupil diameter and area from its focal length and f-number, and compares light-gathering with another f-stop.

## Inputs

- Focal length (mm, cm, m, in, µm)
- f-number N

## Results

- Aperture diameter
- Aperture area
- Stops slower than f/1

## Formula

```
D = f / N,  A = π·D²/4
```

## Explanation

The f-number is the ratio of focal length to aperture diameter. A 50 mm lens at f/2 has a 25 mm aperture; each full stop (×√2 in f-number) halves the light. The aperture area sets how much light reaches the sensor.

### How to use the Aperture Area Calculator

- **Focal length**
- **f-number N**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Enter the focal length and the f-number. The light ratio compares your f-number with f/1.

### Inputs explained

FieldWhat to enterFocal lengthUnits: mm, cm, m, in, µmf-number NA number

### What each result means

- **Aperture diameter** = [Focal length]÷[f-number N]
- **Aperture area** = pi×([Focal length]÷[f-number N])^2÷4
- **Stops slower than f/1** = 2×log([f-number N], 2)

### Example values

How the main result changes when **Focal length** changes and everything else stays at the example values above:

Focal length (mm)Aperture area (mm²)2562.611537.5140.875850250.445862.5391.321675563.50311001,001.7834

## Worked example

Inputs — Focal length: 50 mm; f-number N: 2.8.

Results — Aperture diameter = 17.8571 mm; **Aperture area = 250.4458 mm²**; Stops slower than f/1 = 2.971 stops.

## Key terms

- **f-number**: Focal length divided by aperture diameter.

## FAQ

**What does f/2.8 mean?**
The aperture diameter is the focal length divided by 2.8.

**How much more light does f/2 let in than f/2.8?**
About twice as much (one stop).

**Does a larger f-number mean a smaller hole?**
Yes.

**Why do telephoto lenses have huge front elements?**
A long focal length needs a large diameter for a small f-number.


## Sources

- [OpenStax – University Physics Volume 3](https://openstax.org/details/books/university-physics-volume-3)
- [HyperPhysics (Georgia State University)](http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html)