Free · 2D geometry calculators 📏

Rectangular Face Area & Unit Conversion

Calculate the area of one rectangular face, or a missing side, with metric and customary area units.

Calculator inputs

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Enter the known values in the units shown. Results update as you type.
Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
Use the worked example to check the method. Reset restores the starting fields.

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

A rectangular face 3 m by 4 m has an area of 12 m². This is one flat face; it is not the total exterior area of a box.

Area = length × width; missing side = area ÷ known side

Enter these known values and leave the other values blank.

Both side lengths and area must be positive. The face has four right angles.
This computes one rectangle. A box or other 3D object needs separate areas for its other faces.
The international acre is exactly 43,560 square feet. The soccer-field comparison uses a fixed 7,140 m² rather than an unspecified pitch size.
Dimensions and area can use independent display units. No allowance for waste, holes or overlap is included.

No. It gives one rectangular face. A rectangular box’s full surface area is the sum of all six faces.

Enter the known area and length. The width is the area divided by the length after the selected units are converted.

The international acre is exactly 43560 square international feet; Bookify replaces the rounded captured area factor.