Aperture Area Calculator
Compute the physical aperture area of a camera lens from its focal length and f-number: aperture diameter D = f ÷ N, then area A = π(D/2)². Includes a missing-value solver, mm²/cm²/in² converter, and relative light gathering vs f/1.0.
Honest optics note: D = f/N is the effective entrance-pupil diameter the f-number is defined from (at infinity focus). A real iris can differ slightly by design, but the light-gathering ratio 1/N² is exact.
Aperture area from focal length & f-number
Full-stop table for this focal length
Solve the missing variable
Area unit converter
How the math works (verified)
Worked example — 35 mm lens at f/1.2:
- D = f ÷ N = 35 ÷ 1.2 = 29.166667 mm
- A = π × (D ÷ 2)² = π × 14.583333² = 668.13385 mm²
- Relative gathering = 1 ÷ N² = 1 ÷ 1.44 = 69.444444% of f/1.0
One full stop (f/1.4 → f/2 → f/2.8 …) multiplies the f-number by √2 and halves the aperture area — that is why each stop halves the light.
Not depth of field
This tool computes aperture area — the physical size of the lens opening (light gathering). It does not compute depth of field, hyperfocal distance, or diffraction limits. For those, use our depth-of-field calculator.
Frequently asked questions
What is the aperture area formula?
Aperture diameter D = focal length ÷ f-number, then area A = π × (D ÷ 2)². Example: a 50 mm lens at f/2.8 has D = 50 ÷ 2.8 = 17.857143 mm, so A = π × 8.9285715² = 250.44584 mm².
How much light does f/2.8 gather compared to f/1?
Relative light gathering at the same focal length equals 1 ÷ N². At f/2.8 that is 1 ÷ 7.84 = 12.755102% of the f/1.0 gathering. Each full stop (e.g. f/2.8 → f/4) halves the aperture area.
How do I convert aperture area between mm², cm² and in²?
1 cm² = 100 mm² and 1 in² = 645.16 mm². Example: 250.44584 mm² = 2.5044584 cm² = 0.38819183 in². Use the Unit Converter tab above for any value.
What is the aperture area of an 85 mm f/1.4 lens?
D = 85 ÷ 1.4 = 60.714286 mm, so A = π × 30.357143² = 2895.1539 mm² — about 51.020408% of what the same lens would gather at f/1.0.
Can I solve for a missing value, like the f-number?
Yes. Enter any 3 of area, diameter, focal length and f-number in the Solve Missing tab and the 4th is computed. Example: D = 12.5 mm gives A = 122.71846 mm² (the area of a 50 mm f/4 aperture).
Is aperture area the same as depth of field?
No. Aperture area measures the physical size of the lens opening and how much light it gathers. Depth of field measures the zone of acceptable sharpness in the photo. For depth of field, hyperfocal distance and diffraction limits, use our depth-of-field calculator.
Is the diameter here the physical iris size?
D = f ÷ N is the effective (entrance-pupil) diameter the f-number is defined from, measured at infinity focus. A real lens iris can differ slightly due to optical design and focus breathing, but the light-gathering ratio 1 ÷ N² is exact.
Free tool by NRTechStudio