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Interior measurement

Room Area Calculator

Estimate a rectangular room's floor area, perimeter, metric equivalents, and optional waste-adjusted planning area before buying materials.

Quick mode Enter length and width. Advanced room shapes can be measured in sections.

Use the same unit for length and width. For irregular spaces, calculate each rectangle separately and add the results.

Estimate results

120 sq ft, about 11.15 sq m
Area
120 sq ft
Metric area
11.15 sq m
Perimeter
44 ft
Material planning area
120 sq ft

Visible assumptions

  • Room shape is treated as a rectangle.
  • Length and width use the same unit.
  • Waste factor changes only the material planning area.
Rectangular room area preview A rectangle labeled with room length, room width, area, and perimeter. 12 ft 10 ft 120 sq ft simple rectangular room
Visual preview assumes a rectangular room. Shape, alcoves, closets, and angled walls can change real material needs.

Last reviewed: June 4, 2026

How this calculator works

Enter the room length and width using one unit system. The calculator converts those dimensions into feet and meters, then estimates floor area and perimeter. The optional waste factor is applied only to the material planning area.

Room area formula

Area = Length x Width

Perimeter = 2 x (Length + Width)

Square feet are converted to square meters using 1 square foot = 0.09290304 square meters.

Example calculation

For a 12 ft by 10 ft room, the area is 120 sq ft. That is about 11.15 sq m. The perimeter is 44 ft, or about 13.41 m.

Measuring tips

  • Use a tape measure or laser measure with the same unit throughout the room.
  • Measure along the floor, not across furniture or rugs.
  • Use the longest straight wall-to-wall measurement for each side.
  • Round measurements only after recording the raw value.
  • For L-shaped rooms, split the room into smaller rectangles.
  • Keep closet, alcove, and hallway areas separate if materials differ.

Common room measuring mistakes

  • Mixing feet, inches, meters, and centimeters in one calculation.
  • Measuring furniture placement instead of the actual wall-to-wall room size.
  • Ignoring closets, bay areas, alcoves, or small connected sections.
  • Rounding every measurement too early, which can compound the final estimate.

Room area calculator FAQ

How do I calculate room square footage?

Measure the room length and width in feet, then multiply length by width. A 12 ft by 10 ft room is 120 sq ft.

How do I convert square feet to square meters?

Multiply square feet by 0.09290304. For example, 120 sq ft is about 11.15 sq m.

Should I include closets?

Include closets or alcoves when the same material will cover them. Keep them separate when flooring, paint, or trim choices differ.

Can this calculator handle irregular rooms?

This version treats the room as a rectangle. For L-shaped or irregular rooms, split the space into rectangles and add the areas together.

Can I use this for flooring?

Yes, the area result is a useful starting point for flooring, but flooring projects usually need a waste factor for cuts and layout direction.

Can I use this for paint?

Room floor area helps describe room size, but paint estimates usually need wall area, wall height, coats, doors, and windows.

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