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Rectangle Calculator

Find area, perimeter, diagonal, or a missing dimension from length, width, area, or perimeter.

Clear formulas
Educational steps
Detail breakdown

Rectangle solve modes recover missing sides when area or perimeter is known.

Limitation: Educational geometry.

Jump to calculator · Sources & review

How to Use the Rectangle Calculator

Rectangle solve modes recover missing sides when area or perimeter is known.

1

Open the Rectangle calculator and read field labels.

Match the mode

Educational geometry.

What It Calculates

Rectangle solve modes recover missing sides when area or perimeter is known.

Worked Examples

8 × 5 rectangle

Inputs

solveFor:from_sides
length:8
width:5

Result

Area 40

P = 26; diagonal ≈ 9.434.

Area 40, length 8

Inputs

solveFor:from_area_length
length:8
area:40

Result

width 5

40 ÷ 8 = 5.

P = 26, length 8

Inputs

solveFor:from_perimeter_length
length:8
perimeter:26

Result

width 5

26/2 − 8 = 5.

Check your mode

Educational geometry.

Frequently Asked Questions

Yes. Results keep the precision shown on the page unless the engine requires integers.

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Formulas

Standard definitions with assumptions noted below.

Formula

A ​=​ lw; P ​=​ 2​(​l​+​w​)​

Scientific Background

Standard geometry definitions with assumptions stated on-page. Educational only—not professional certification.

Sources & review

Rectangle Calculator documents the references behind its formulas and assumptions. Always treat results as educational estimates, not personalized professional advice.

Last reviewed

July 22, 2026

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