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Camera Aperture (f-stop) Converter

Science

Convert a camera f-number to the number of stops down from f/1.0 and its relative light transmission — for photographers comparing lens aperture values.

Reviewed by the thecalcu.com team · Last updated July 16, 2026

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What is a Aperture?

A Camera Aperture Converter translates between a lens's f-number (the familiar "f/2.8" or "f/8" rating) and two related photographic measurements: how many full stops it is from a maximally wide f/1.0 aperture, and how much light it actually transmits relative to that reference point. Because f-numbers follow a geometric, not linear, progression, mentally comparing two aperture settings (like "how much more light does f/1.8 let in than f/5.6?") requires working with squares and square roots that most photographers don't calculate by hand.

This tool makes that comparison instant, which is useful alongside the Illumination Converter when working through a full exposure calculation involving aperture, shutter speed, and ISO together.

Why Use a Camera Aperture Converter?

Photography and cinematography both rely on precise light control, and aperture is one of three exposure variables (alongside shutter speed and ISO) that photographers adjust in full or partial stops. Comparing lenses with different maximum apertures, or calculating how much to compensate shutter speed or ISO when changing aperture, requires knowing the exact stop difference, not just that one f-number is "bigger" than another.

Two concrete situations this solves: comparing a new lens's f/1.4 maximum aperture against your current f/2.8 lens to know exactly how many stops (and how much more light) you're gaining, and calculating the relative light transmission of a specific f-stop to cross-check an exposure calculation.

Who Should Use This Converter?

  • Photographers comparing lens specifications or calculating exposure compensation when switching between different aperture settings.
  • Videographers and cinematographers working through exposure calculations that require precise stop-based light comparisons.
  • Photography students learning the mathematical relationship between f-stop, aperture area, and light transmission.
  • Camera and lens buyers evaluating how much "faster" (more light-gathering) one lens is compared to another based on their maximum aperture ratings.
  • Astrophotographers calculating light-gathering differences between telescope or lens apertures for exposure planning.

What Insights Does the Aperture Converter Give You?

Converting to Stops Down from f/1.0 tells you exactly how many photographic stops separate your aperture setting from the widest reference point, which is the standard unit photographers use to compare exposure changes across aperture, shutter speed, and ISO. Converting to Relative Light Transmission gives you the precise fraction of light passed compared to f/1.0, useful for detailed exposure calculations or verifying manufacturer specifications.

Because f-stops follow a square-law relationship rather than a linear one, small-looking differences in f-number (like f/2.8 to f/4) actually represent a full stop, a 50% change in light, which these converted values make explicit rather than leaving to intuition.

How to use this Aperture calculator

  1. Select your starting unit from the From dropdown, f-number (f/N), Stops Down from f/1.0, or Relative Light Transmission.
  2. Enter your value, such as 2.8 for an f/2.8 aperture.
  3. Select your target unit from the To dropdown, such as Stops Down from f/1.0.
  4. Read the converted result, which updates instantly.
  5. Repeat with a second aperture value to compare the light-transmission difference between two lenses or settings.
  6. Use the swap (⇅) button to reverse the conversion direction if needed.

Formula & Methodology

All conversions route through the f-number (N) as the canonical unit, based on the standard photographic relationship that aperture area, and light transmitted, is proportional to 1/N²:

Stops from f/1.0 = 2 × log₂(N)  |  N = 2^(Stops ÷ 2)
Relative Light Transmission = 1 ÷ N²  |  N = 1 ÷ √(Relative Light Transmission)

Worked example: Converting f/4 to relative light transmission, 1 ÷ 4² = 1 ÷ 16 = 0.0625, meaning f/4 transmits 6.25% of the light that f/1.0 would. Converting f/4 to stops: 2 × log₂(4) = 2 × 2 = 4 stops down from f/1.0, confirming the well-known fact that f/4 is exactly 4 full stops narrower than a fully open f/1.0 lens.

Frequently Asked Questions

An f-stop (or f-number) describes a camera lens's aperture size as a ratio of the lens's focal length to the diameter of its opening, written as f/N, for example, f/2.8 or f/8. A smaller f-number means a wider opening that lets in more light, while a larger f-number means a narrower opening that lets in less light.
Each full photographic stop corresponds to the f-number changing by a factor of √2 (approximately 1.414), because aperture area, and therefore light, is proportional to 1/f-number². The formula is: stops down from f/1.0 = 2 × log₂(f-number).
Select f-number (f/N) as your From unit and Relative Light Transmission as your To unit, then enter your f-stop value. The tool calculates 1 ÷ f-number², giving the fraction of light passed compared to a fully open f/1.0 lens, for example, f/2.8 transmits about 12.8% of the light that f/1.0 would.
Going from f/4 to f/2.8 is exactly one full stop, and each full stop doubles (or halves) the amount of light reaching the sensor. This is why the standard full-stop sequence, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, has each value roughly 1.414× the previous one rather than increasing in even steps.
Using the formula stops = 2 × log₂(f-number), f/1.8 is about 1.17 stops from f/1.0, and f/8 is about 6 stops from f/1.0, so the difference is approximately 4.83 stops, meaning f/1.8 lets in roughly 28 times more light than f/8. Enter both values into this converter's Stops Down from f/1.0 unit to verify this directly.
F-stop is a purely geometric calculation based on the lens's focal length and aperture diameter, while T-stop (transmission stop) accounts for actual light loss due to the lens elements and coatings, making it more accurate for cinema and video work where exact exposure matching across lenses matters. This converter calculates the theoretical f-stop relationship only, since T-stop requires knowing a specific lens's measured transmission efficiency, which varies by lens.
The f-number is a ratio, focal length divided by aperture diameter, so for a fixed focal length, a larger aperture diameter (more light) produces a smaller f-number, and a smaller aperture diameter (less light) produces a larger f-number. This inverse relationship is why f/1.4 (wide open, more light) is numerically smaller than f/16 (narrow, less light).
Select your starting unit, f-number, Stops Down from f/1.0, or Relative Light Transmission, enter your value, then select the unit you want to convert to. The result updates instantly, letting you compare exposure differences between any two aperture settings.
Lenses with a maximum aperture of f/1.8, f/1.4, or wider are generally considered 'fast,' since they let in significantly more light than typical kit lenses (often f/3.5-5.6), which helps in low light and enables a shallower depth of field. This converter shows exactly how many stops faster one lens is compared to another using their maximum f-number.
Yes, a wider aperture (lower f-number) produces a shallower depth of field, keeping less of the scene in focus, while a narrower aperture (higher f-number) produces a deeper depth of field with more of the scene in focus. This converter calculates only the light-transmission relationship between f-stops; depth of field also depends on focal length and subject distance, which aren't part of this conversion.
Also known as
f-stop converteraperture to stopsf-number to light valuecamera aperture calculatorstops to f-stopaperture light transmission converter