Area Calculator for Feet and Inches

An area calculator for feet and inches works out the area of a rectangle or square when you enter its length and width in feet and inches. It returns the result in square feet, with an optional square-inch equivalent, so you can estimate a floor, wall, patio, or other flat surface.

Formula

For a rectangle, multiply its length by its width after converting each measurement to the same unit. This calculator converts the feet-and-inches entries to decimal feet, then multiplies them:

Area (ft²) = (L + Li ÷ 12) × (W + Wi ÷ 12)

• L is the length in feet.
• Li is the additional length in inches.
• W is the width in feet.
• Wi is the additional width in inches.
• 12 is the number of inches in one foot.

To convert square feet to square inches, multiply by 144 because one square foot is 12 inches × 12 inches, or 144 square inches. The first result is rounded to two decimal places; the square-inch result is displayed to the nearest whole square inch.

Worked Example

Using the calculator’s default measurements, the length is 12 feet 0 inches and the width is 10 feet 0 inches.

1. Convert the length to decimal feet: 12 + 0 ÷ 12 = 12 ft.
2. Convert the width to decimal feet: 10 + 0 ÷ 12 = 10 ft.
3. Multiply: 12 × 10 = 120 ft².
4. Convert to square inches: 120 × 144 = 17,280 in².

The result is 120.00 square feet, or 17,280 square inches.

When to Use an Area Calculator

Use this calculation when a surface has a rectangular or square shape and you know its two perpendicular dimensions. Common uses include estimating floor area, measuring a rectangular garden bed, checking a tabletop’s surface, or finding the area of a wall section. The method gives the area of the face or surface, not the volume of a room or the amount of material needed after accounting for waste, seams, or obstructions.

For a square, enter the same measurement for length and width. For example, a square measuring 8 feet on each side has an area of 8 × 8 = 64 square feet. Do not add the sides together: that gives perimeter, which measures the distance around the shape, not the area it covers.

Metric measurements use the same principle. If both dimensions are in metres, multiply them to get square metres (m²); if both are in centimetres, the result is square centimetres (cm²). To convert square feet to square metres, multiply by approximately 0.092903. To convert square metres to square feet, multiply by approximately 10.7639. Convert the dimensions before multiplying, or convert the final area using the appropriate squared-unit factor.

How to Measure Feet and Inches

Measure the longest side as the length and the perpendicular side as the width. Record each measurement in feet and any remaining inches. For example, 9 feet 6 inches should be entered as 9 in the feet field and 6 in the inches field—not as 9.6 feet. Six inches is half a foot, so that measurement is 9.5 feet in decimal form.

• Measure between the edges that define the surface, keeping the tape straight.
• Use the same reference points for both dimensions; include a feature only if it belongs to the area you intend to cover.
• For better results on an irregular or large surface, measure in sections rather than relying on one estimated width.
• Enter the leftover inches separately. Inches must be less than 12; 12 inches is one additional foot.

Irregular Shapes and Material Estimates

This calculator assumes the surface is a single rectangle. For an L-shaped room or another irregular outline, divide it into rectangles, calculate each rectangle separately, and add the areas. If a section is excluded, such as a rectangular opening, calculate its area and subtract it. Avoid counting an overlapping part twice.

For a triangle, multiply its base by its perpendicular height and divide by two. For a circle, use π multiplied by the radius squared. These are different formulas, so a rectangle calculator should not be used by treating a circle’s diameter or an irregular room’s maximum dimensions as though they described a full rectangle.

An area result can help you plan materials, but it is not automatically the order quantity. Flooring, tile, sod, paint, and other products have different coverage, packaging, installation patterns, and recommended allowances. Check the product’s stated coverage and instructions. For items sold only in whole packages, divide the required area by the package coverage and round up to the next whole package; account separately for cuts, defects, or future repairs where appropriate.

Common Measurement and Rounding Mistakes

• Mixing units: Multiplying feet by inches produces square foot-inches, not square feet. Convert both dimensions to feet first, or convert both to inches and calculate square inches.
• Reading inches as decimal feet: 5 feet 8 inches is 5 + 8 ÷ 12 = 5.6667 feet, not 5.8 feet.
• Confusing area and perimeter: Area is length × width and is reported in square units. Perimeter is the sum of the sides and is reported in ordinary units such as feet.
• Rounding too early: Keep the original measurements through the calculation and round the final result. Early rounding can create noticeable differences across many sections.
• Assuming the bounding rectangle is usable area: Built-ins, cutouts, angled walls, and inaccessible sections may change how much surface actually needs coverage.

At very small scales, measurement precision matters: a small error in either dimension changes the calculated area. At larger scales, measure more than once and split complicated layouts into manageable shapes. The formula itself does not account for uneven surfaces or installation waste.

Frequently Asked Questions

How do I calculate square feet from feet and inches?
Convert each dimension to decimal feet by dividing its inches portion by 12 and adding that to the feet. Multiply the converted length by the converted width.

What is 10 feet by 12 feet in square feet?
Multiply 10 by 12. The area is 120 square feet.

How many square feet are in one square foot?
One square foot equals 144 square inches, since a square foot measures 12 inches by 12 inches.

Can I use this calculator for a room with an alcove?
For a rectangular alcove, calculate the main rectangle and the alcove separately, then add their areas if both are part of the surface. For a cutout, subtract its area instead.

Is square footage the same as the amount of flooring to buy?
No. Square footage describes the measured surface. The purchase quantity also depends on package coverage, layout, cuts, and the product’s instructions, so use the result as a planning measurement rather than a guaranteed order quantity.

Related

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in l | Length | ft | 12 | 0 | 100000
in li | Length inches | in | 0 | 0 | 11.999999
in w | Width | ft | 10 | 0 | 100000
in wi | Width inches | in | 0 | 0 | 11.999999
out area | Area | ft² | (l + li / 12) * (w + wi / 12) | 2
out inch | Area | in² | area * 144 | 0