Square Footage Calculator

Square footage is a unit of area, but it does not say what the area represents. A room's usable floor, a flooring finish, a wall face, a roof surface, a planting bed, a lawn, a property listing, and a legal parcel can all be measured differently. Write the purpose on the sketch before choosing a formula, then mark the boundaries, included parts, and exclusions that matter for that purpose.

For a material takeoff, divide irregular layouts into simple, non-overlapping shapes. Retain a small area ledger instead of entering a large unexplained total. The same approach is used in How to Calculate Yardage when a measured surface later becomes a volume calculation. Area is the beginning of that workflow, not proof that a material quantity or design is correct.

An area formula can sometimes use fewer facts than a perimeter. The triangle tab calculates area from a perpendicular base and height, but the displayed perimeter assumes those values are the two legs of a right triangle. For 12 ft base and 9 ft height, it calculates 54 sq ft of area and a 36 ft perimeter because the assumed hypotenuse is 15 ft. If the real triangle is not right-angled, its area may still be correct while its displayed perimeter is not.

The trapezoid tab has a similar boundary. It calculates area from the two parallel bases and height, but its perimeter assumes a symmetrical isosceles layout. With 20 ft and 10 ft bases and 8 ft height, the page calculates 120 sq ft, then assumes two 9.434 ft sloping sides for a perimeter of about 48.868 ft. Do not use that number for a fence, edging, trim, flashing, or material order unless the actual trapezoid has that symmetry.

The L-shape tab simply adds two entered rectangles. That is useful only when the boxes do not overlap. If both boxes include the same corner, the overlap is counted twice. Its perimeter model also assumes a side-by-side connection and removes twice the smaller entered width as the shared edge. Draw the two components before using the result.

Room Builder is a different tool: it sums the areas of rooms you add. It also sums each room's individual perimeter, so a wall shared by two rooms appears twice. This is not the exterior perimeter of the suite, a baseboard quantity, a paintable wall area, or a legal room schedule. Use it as an area ledger, then measure any product-specific length or wall surface separately.

For a lawn, retain beds and hardscape as exclusions and use the Sod Calculator only after the plantable area is defined. For floor products, use the Flooring Calculator or Tile Calculator with the actual package coverage and layout plan.

The slider applies the same simple formula to every selected shape: gross area = net area × (1 + entered percentage). It does not know grain direction, tile layout, pattern repeat, diagonal cuts, roll width, seam placement, damage, package increments, room transitions, openings, or reusable offcuts. A fixed 10% is therefore not a universal material recommendation.

Calculate the net geometry first. Then identify the actual product, package coverage, installation direction, cut plan, and supplier policy before choosing an allowance. Keep the allowance separate from the measurements so another person can see what changed if the layout or product changes. The illustration below is a useful final check: geometry, exclusions, product coverage, and ordering are different decisions.

Custom Area accepts an existing area in square feet, square yards, square meters, acres, or hectares and converts it to square feet before applying any area allowance. It intentionally reports no perimeter because an area alone cannot determine a boundary. A 500 sq ft square, a long narrow strip, and an irregular curve can have the same area with very different edges and material needs.

This page does not survey a parcel, certify a real-estate listing, determine building-code area, estimate paint coverage, select flooring, calculate roof surface, or replace a measured project plan. Confirm the measurement purpose and standard with the responsible project parties. If an input, shape model, or result appears unclear, you can report a calculator issue for review.