Can I use it for aspect ratios?

Yes, that is one of the main uses. 1920 by 1080 simplifies to 16 by 9, and scaling the first number to 1280 gives 720 for the second. That is the whole calculation behind resizing something without distorting it.

What happens with decimals?

They work, and the ratio is not reduced, because there is no common divisor to reduce by in the usual sense. You still get the decimal, the one to n form and the shares, which are the useful parts for a non whole ratio.

What is the one to n form for?

Comparing ratios that do not share a common factor. Two ratios written as 1 to something can be compared at a glance in a way that 17 to 5 and 22 to 7 cannot.

Ratio Calculator

Simplify a ratio, or scale one side of it.

First number

Second number

Scale the first number to

Simplify a ratio, or scale one side of it.

How to use it

Enter both numbers. A width and a height, or any two quantities.
Read the simplified form. Plus the decimal and each side as a share of the whole.
Scale one side. Give a new first number and the second follows the proportion.

When you would use this

A ratio is two numbers and every question about it is a different way of writing them. The simplified form is what people usually want: 1920 to 1080 is 16 to 9, and seeing that is the point. The decimal, the one to n form and the two shares as percentages answer the other three questions, and they cost nothing to show alongside. Scaling is the operation that gets used most and is easiest to get wrong in your head. Give a new first number and the second follows the proportion exactly, which is the arithmetic behind resizing an image without distorting it, or behind multiplying a recipe. Decimals are accepted and not reduced, because reducing them in the usual sense is not meaningful. The decimal, the one to n form and the shares are all still correct and are the useful parts of a non whole ratio. A ratio to zero is refused rather than answered, since nothing is in proportion to nothing.

Questions

Can I use it for aspect ratios?: Yes, that is one of the main uses. 1920 by 1080 simplifies to 16 by 9, and scaling the first number to 1280 gives 720 for the second. That is the whole calculation behind resizing something without distorting it.
What happens with decimals?: They work, and the ratio is not reduced, because there is no common divisor to reduce by in the usual sense. You still get the decimal, the one to n form and the shares, which are the useful parts for a non whole ratio.
What is the one to n form for?: Comparing ratios that do not share a common factor. Two ratios written as 1 to something can be compared at a glance in a way that 17 to 5 and 22 to 7 cannot.