Construction & DIY
Square Footage Calculator
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How to use it
Using the square footage calculator
- 01
Measure each rectangle
Record length and width in feet for every distinct area; rooms, wings, or sections of a lot.
- 02
Fill one to three sections
Unused optional fields stay blank; both values of a section are required when used.
- 03
Read the total
The primary result is combined square feet; check the acres row for property-sized measurements.
Good to know
Breaking irregular shapes down
Almost no real floor plan is one clean rectangle. The professional habit is decomposition: split the space into overlapping-free rectangles, measure each, and let the arithmetic sum them. Three sections cover the vast majority of homes and apartments.
Square feet vs acres
Rooms live in square feet; land lives in acres. Because an acre spans 43,560 sq ft; bigger than four NHL rinks; the conversion row keeps a large lot measurement from feeling abstract.
Where accuracy pays
Flooring orders, heating-load estimates and appraisals all key off this number. Measuring to the inch rather than rounding to the foot routinely swings totals by 2–3%; enough to leave pallets of laminate short.
How it's calculated
The math behind this calculator
Total = Σ Lengthᵢ × Widthᵢ Acres = Total ÷ 43,560Every filled section contributes its length × width rectangle to the running total. Leave unused sections blank. An acre is exactly 43,560 square feet, so the acres row simply divides the total; handy when measuring lots rather than rooms.
Assumptions & limitations
- Sections are true rectangles; L-shaped spaces should be split and entered section by section.
- Measurements are interior for floor areas or property-line for lots.
- Closets, bays and stair treads counted only if entered explicitly.
Worked example
A 30×20 great room plus a 15×15 office totals 600 + 225 = 825 square feet; about 0.0189 acres of floor space.
FAQ
Frequently asked questions
- How do I measure an L-shaped room?
- Split it into two rectangles where they meet, measure each fully, and enter them as separate sections.
- How many square feet is an acre?
- Exactly 43,560. A football-field-sized lot of about half an acre holds roughly 21,780 sq ft.
- Should I include closets?
- For flooring, yes; they take material too. Enter closets as their own small sections.
- Do I measure inside or outside walls?
- Inside faces for flooring and painting; outside dimensions for property and appraisal figures.
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