🔺 Exposure Triangle Calculator

Enter your original exposure settings, then change one setting to see the equivalent adjustment needed in another to maintain the same overall exposure.

Original ISO

Original Aperture (f-number)

Original Shutter (seconds)

New ISO

New Aperture (f-number)

Every change is converted to stops

A stop is a doubling or halving of light, so the arithmetic is all base-2 logarithms. ISO scales directly with light; aperture scales with the square of the f-number, because it is the area of the opening that matters.

ISO stops      = log2(ISO2 / ISO1)
aperture stops = log2(N1² / N2²) = 2 × log2(N1 / N2)
new shutter    = old shutter / 2^(ISO stops + aperture stops)

The defaults show it: ISO 100 to 400 is log2(4) = +2.00 stops, the aperture stays at f/8 for +0.00, and 1/125 s divided by 2² gives 1/500 s. Gaining light makes the number positive and the shutter faster; losing it does the reverse.

Filling the boxes in

Shutter goes in as a decimal. 1/125 is 0.008, 1/1000 is 0.001, half a second is 0.5.
Shutter is the only thing solved for. To find an equivalent aperture instead, nudge the new f-number until the shutter it returns is the one you want on the dial.
Full-stop ladders - ISO 100, 200, 400, 800; f/2.8, f/4, f/5.6, f/8 (each ×√2); 1/500, 1/250, 1/125, 1/60.

Any result under a second is printed as 1/n, rounded to a whole denominator. A computed 0.6 s therefore reads 1/2 s - check the decimal in your head near the one-second mark.

Frequently asked questions

How many stops is f/2.8 to f/8?

Three. The tool returns -3.03 because f/2.8 is a rounded label for 2√2 = 2.828; type 2.83 and it comes out at exactly -3.00 stops.

What shutter speed replaces ISO 100 with ISO 400?

Two stops faster: at f/8, 1/125 s becomes 1/500 s. The aperture is untouched, so depth of field is identical and only noise changes. The maths is exact rather than dial-rounded, so 1/60 s comes back as 1/240 s - set 1/250.

Can I change ISO and aperture at the same time?

Yes - the two stop figures are added before the shutter is worked out. ISO 100 to 400 (+2) with f/8 to f/16 (-2) cancels out, so 1/125 s stays 1/125 s.