An f-stop (or f-number) is the ratio of a lens focal length to its entrance pupil diameter. Each full stop either halves or doubles the light: f/1.4 lets in twice as much light as f/2, f/2 twice as much as f/2.8, and so on.

What is Exposure Value (EV)?

EV is a single number that represents a combination of aperture and shutter speed at ISO 100. Any two settings with the same EV produce the same exposure brightness. EV 0 is f/1 at 1 second at ISO 100; each +1 EV halves the light.

What does equivalent exposure mean?

Equivalent exposures are different combinations of aperture, shutter speed, and ISO that result in the same sensor exposure level. They produce the same brightness but different optical effects — depth of field, motion blur, and noise differ.

How many stops is f/2.8 vs f/4?

f/2.8 to f/4 is exactly one full stop. f/4 lets in half the light of f/2.8. The ratio between adjacent full f-stops is always √2 ≈ 1.41.

What are the standard full f-stops?

The standard full f-stop sequence is: f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45, f/64. Each step is √2 × the previous value.

F-Stop Calculator

Find equivalent exposures by comparing aperture, shutter speed, and ISO combinations that share the same exposure value (EV).

Reference Exposure

Aperture (f-number)

Shutter Speed

ISO

Exposure Value

—

ISO-adjusted EV

Equivalent Exposures

Same EV — different aperture, shutter, and ISO combinations

Aperture	Shutter	ISO
Loading...

Full F-Stop Scale

Standard aperture values with full, half, and third stops

f-number	Stop type	Stops from f/1	Light (relative)

Summary

Find equivalent exposures by comparing aperture, shutter speed, and ISO combinations that share the same exposure value (EV).

How it works

Enter a reference aperture (f-number), shutter speed, and ISO.
The calculator computes the Exposure Value (EV) using the APEX formula: EV = log2(N² / t) - log2(ISO/100).
All standard aperture, shutter speed, and ISO combinations matching that EV are listed.
Browse the equivalent combinations — any row gives the same exposure.
Scroll down for the complete f-stop scale table showing full, half, and third stops.

Use cases

Switch from a wide aperture to a smaller one while keeping exposure the same by adjusting shutter speed.
Find a faster shutter speed for action shots without changing exposure.
Determine what ISO change compensates for a shutter speed limit on a gimbal.
Understand how each f-stop doubles or halves the light reaching the sensor.
Teach exposure triangle concepts with a clear visual reference.
Plan a long-exposure substitution: same EV at f/16 and a 30-second shutter.

Frequently Asked Questions

Last updated: 2026-09-22 · Reviewed by Nham Vu