Square Feet Calculator — Rooms & Floor Plans
Calculate square feet for one room or a full floor plan in exact feet and inches. Add rooms by floor, subtract excluded areas, and estimate materials and cost.
Building square footage in feet and inches
Measure the outside footprint for gross building area, or use one room at a time for finished interior area. Inches are converted correctly—not treated as decimal feet.
30 ft 6 in × 20 ft 3 in × 2 floors = 1,235.25 sq ft
Footprint vs. total: a 600 sq ft two-story building usually has about 1,200 sq ft of gross floor area, not a 1,200 sq ft footprint. For an irregular building, calculate and add each rectangle separately below.
Floor plan area calculator — add rooms by floor
Measure each room exactly in feet and inches, assign it to a floor, and subtract stairs, voids or other excluded sections. Split an L-shaped room into two rows.
Blocks are scaled by relative room area and labeled by floor. Excluded sections use a dashed amber outline and are subtracted from the net total.
Calculate area and perimeter for a shape
Choose one of ten shapes, enter dimensions in any supported length unit, and convert the area instantly.
Total square footage for rooms and project sections
Add measured sections, subtract stairs or cutouts, then include material overage, package coverage, and price.
Calculate interior wall surface area
Use room perimeter and height, subtract the combined door and window opening area, then add an optional overage.
Estimate sloped roof surface area
Start with the horizontal footprint, add equal eave overhang, and apply a rise-per-12 pitch factor plus waste.
Area of an irregular polygon from coordinates
Enter boundary points in order around a floor, lot, or drawing. The shoelace formula calculates area, perimeter, centroid, and orientation.
Shape diagram
Calculation
Area details
Square feet calculator for rooms and floor plans
Add every rectangular room in feet and inches, assign it to the main floor, upper floor or basement, and subtract stair openings, voids or excluded sections. The live floor subtotals make a missing room or double-counted space easier to spot.
Area calculator for common shapes
Calculate rectangles, squares, circles, right triangles, trapezoids, parallelograms, ellipses, sectors, annuli, and regular polygons with perimeter and unit conversions.
Wall and roof area calculators
Wall mode uses room perimeter × height minus door and window openings. Roof mode converts a horizontal footprint to sloped surface area with a rise-per-12 factor and optional overhang.
Land and irregular polygon area
Coordinate mode applies the shoelace formula to three through twenty boundary points. It also reports perimeter, centroid, orientation, square feet, acres, and hectares.
Use your square footage for a material estimate
Once the room or floor-plan total is ready, continue with the tile and box calculator, paint coverage calculator, concrete slab calculator, or wallpaper roll calculator. Each tool applies its own waste, package and geometry rules instead of treating every square foot as interchangeable.
Frequently asked questions
How do I calculate square footage from a floor plan?
Measure each enclosed room or rectangular section, multiply length by width, and add the room areas by floor. Subtract only openings or sections that were included in another measurement. Keep exterior-footprint area separate from interior room totals because wall thickness and area rules differ.
How do I enter an L-shaped room?
Split the L into two non-overlapping rectangles and add both rows to the same floor. If you measured one large outer rectangle instead, add the rectangle and enter the missing corner as Subtract / exclude.
How much flooring waste should I add?
Simple straight installations often use 5% to 10%, while diagonal layouts, irregular rooms, and pattern matching may need more. Follow the product and installer guidance.
What is a roofing square?
One roofing square equals 100 square feet of roof surface. The calculator reports squares after pitch, overhang, and waste are applied.
Do coordinate points need to close the polygon?
No. Enter each corner once in clockwise or counterclockwise order; the calculator automatically connects the final point back to the first.
Measurement notes
Room-by-room totals are planning estimates, not certified living-area measurements. Real-estate and appraisal standards may treat stairs, basements, garages, low ceilings and exterior wall thickness differently. Confirm dimensions on site and follow the applicable measurement standard before publishing or purchasing materials.
