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Aperture F Stop Calculator

Work out aperture f stop instantly with clear inputs, formula shown and shareable results.

About Aperture F Stop Calculator

Because light passing an aperture depends on its area, one stop changes the f-number by the square root of two, so the new f-number is the old times 2 to the power of stops over two. That square root is why the f-stop sequence runs 1.4, 2, 2.8, 4 rather than doubling, and why closing one stop halves the light rather than the diameter.

Formulas

Aperture change

new f-number = current f-number x 2 ^ (stops / 2)

Light change

light ratio = 2 ^ (-stops)

Worked example

With the default values below, Aperture F Stop Calculator returns New f-number of 7.920. Change any input above and every figure here is recalculated in your browser.

Inputs used

Current f-numberminimum 0.5 f
5.6 f
Stops to changeaccepts -10–10
1

Results

New f-number
7.920 f
Change in light gathering area
0.5000
Change in light admitted
-50.00%
Nearest marked stop
7.9 f

Step by step

  1. 1Values used
  2. 2Aperture change
  3. 3Light change
  4. 4New f-number= 7.920 f
  5. 5Change in light gathering area= 0.5000
  6. 6Change in light admitted= -50.00
  7. 7Nearest marked stop= 7.9 f

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Aperture F Stop figure worked out?

new f-number = current f-number x 2 ^ (stops / 2). Because light passing an aperture depends on its area, one stop changes the f-number by the square root of two, so the new f-number is the old times 2 to the power of stops over two.

Why does this matter?

That square root is why the f-stop sequence runs 1.4, 2, 2.8, 4 rather than doubling, and why closing one stop halves the light rather than the diameter.

What do I need to enter?

Enter current f-number, stops to change. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.

Related Calculators

Aperture F Stop Calculator – Calculate New f-number