Width of Rectangle Calculator

How to Find Rectangle Width

A rectangle has two unique side lengths: length and width. If you know one side and one additional measurement, you can solve for the missing width using basic geometry formulas.

Width Formulas

Known Values	Width Formula
Length $h$ and Area $A$	$w = A / h$
Length $h$ and Perimeter $P$	$w = P/2 - h$
Length $h$ and Diagonal $d$	$w = \sqrt{d^2 - h^2}$

Worked Example

A rectangle has length $h = 4$ m and area $A = 20$ m².

$$w = \frac{A}{h} = \frac{20}{4} = 5 \text{ m}$$

Frequently Asked Questions

Which side is width and which is length?

By convention, width is often the shorter side, but this calculator treats your entered length as the known side and solves for the other dimension.

What if the diagonal is shorter than the length?

That is impossible for a real rectangle. The diagonal must always be longer than either side.

Can I use this with feet or inches?

Yes. Choose your unit and keep both inputs in the same unit system.

Does this calculator also return area and perimeter?

Yes. After width is found, the tool also displays area, perimeter, and diagonal for the full rectangle.

Known Values	Width Formula
Length \(h\) and Area \(A\)	\(w = A / h\)
Length \(h\) and Perimeter \(P\)	\(w = P/2 - h\)
Length \(h\) and Diagonal \(d\)	\(w = \sqrt{d^2 - h^2}\)

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How to Find Rectangle Width

Width Formulas

Worked Example

Frequently Asked Questions

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