Measure aperture values from focal length inputs. Review diameter, stops, and relative light changes easily. See clear graphs, exports, examples, and practical guidance below.
Choose a mode, enter the required values, and submit. The calculation result appears above this form.
N = f / D
Where N is the f-number, f is focal length, and D is the entrance pupil diameter.
D = f / N
Use this when focal length and target f-number are known and you need the entrance pupil diameter.
f = N × D
Use this when the f-number and aperture diameter are known and you want the focal length.
Light Ratio = (NB / NA)²
This gives the brightness of Aperture A relative to Aperture B.
Stops = 2 × log₂(NB / NA)
A positive value means Aperture A gathers more light than Aperture B.
Choose the mode that matches your goal. Use focal length and diameter to find f-number, or reverse the process for lens planning.
For aperture comparisons, enter two f-numbers. The tool returns light ratio, percentage difference, and stop difference.
If you add a comparison focal length, the calculator also estimates the entrance pupil diameter for both apertures at that focal length.
After submitting, review the result cards above the form, inspect the graph, and export the calculation as CSV or PDF.
| Scenario | Focal Length (mm) | Aperture Diameter (mm) | F-Number | Note |
|---|---|---|---|---|
| Standard portrait lens | 85 | 30.36 | f/2.8 | Balanced brightness and depth control. |
| Low-light prime example | 50 | 35.71 | f/1.4 | Very bright aperture for darker scenes. |
| Landscape setting | 24 | 3.00 | f/8 | Greater depth of field. |
| Telephoto daylight setup | 200 | 25.00 | f/8 | Common stop for sharp outdoor work. |
| Comparison example | 50 | 17.86 | f/2.8 | Twice the light of f/4. |
Aperture describes the effective opening through which light enters the lens. It controls exposure brightness and strongly influences depth of field and background blur.
The f-number is focal length divided by aperture diameter. A smaller f-number means a larger opening, so more light reaches the sensor during the same exposure time.
Yes, approximately. Each full stop changes light by a factor of two. Moving from f/2.8 to f/2 lets in about twice as much light.
It is the apparent size of the aperture opening as seen through the front of the lens. This value is used in the f-number relationship.
Comparing apertures helps estimate exposure changes, brightness differences, and stop shifts. It is useful when switching lenses or adjusting settings for the same scene.
No. It explains aperture relationships and exposure ratios, but real scenes still depend on shutter speed, ISO, lighting conditions, and lens transmission losses.
Common full-stop apertures such as f/1.4, f/2, f/2.8, and f/4 are widely used in photography. Matching them helps you choose practical settings quickly.
Yes. The calculator assumes focal length and aperture diameter use the same unit system. Millimeters are standard and keep the f-number dimensionless.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.