AtlasCalcsUtility Calculation Suite
2026-09-23 9 min read

Square Footage Calculator

Calculate the square footage of rectangles, circles, triangles, trapezoids and more — with live diagram, material and cost plans, and unit conversion.

Calculator

Shape

Quick presets

Length(Feet) Help
Feet

Longest wall, wall to wall

Width(Feet)
Feet
Quantity(areas) Help
areas

Identical rooms or sections

Price (optional)(per square foot) Help
$

Leave blank for area only

Input unit
Price per

Shape diagram

Sketch of the rectangle with your dimensions. Not to scale — verify on site before ordering.

Material takeoff plan

MaterialOrder
Laminate / vinyl flooring (20 sq ft per box)covers 110.00 sq ft incl. 10% waste6 boxes
12×12 in tiles (1 sq ft each)incl. 15% cutting waste115 tiles
Interior paint (350 sq ft per gallon, 1 coat)double for 2 coats1 gal
Plywood sheets (32 sq ft each)incl. 10% waste4 sheets

Cost plan

Materials (@ $5/sq ft allowance)$500.00
Labor & install (@ ~$3/sq ft)$300.00
Contingency (10%)$80.00
Project total$880.00

Estimates only — get 2–3 local quotes. Labor varies by region and finish level.

Real-world comparisons

Parking spaces (≈162 sq ft)0.62
Plywood sheets (32 sq ft)3.13
Paint gallons (350 sq ft/gal)0.29
Share of an acre0.230%

Results

Normal

Total area

100.00sq ft

Rectangle × 1 in feet

Square yards

11.11sq yd

Divide square feet by 9

Square meters

9.29sq m

Divide square feet by 10.764

Square inches

14,400sq in

Multiply square feet by 144

Acres

2.2957e-3ac

Divide square feet by 43,560

Live results update as you type — currently showing 100.00 sq ft for a rectangle measured in feet. Replace the defaults with your own measurements for an exact takeoff.

Visualizations

Your area vs common spaces (sq ft)

100Your area
120Bedroom
300Living room
4002-car garage
4,700Basketball court

Net area vs waste allowance (10%)

Net area91%
Waste (10%)9%

Formula

The area of a rectangle is its length multiplied by its width, both measured in the same unit. Currently showing the rectangle formula — switch shapes above and this section follows.

A = L × W

Variables

SymbolNameUnitDescription
AAreasq ftTotal enclosed area in square feet.
L, W, b, hLinear dimensionsfeetLengths entered above; converted to feet before the formula is applied.
qQuantitycountNumber of identical areas; the single-shape result is multiplied by q.

Explanation

Every path converts your inputs to feet first, applies the shape formula at full precision, then multiplies by quantity. Conversions to sq yd, sq m and acres are exact division.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Convert each dimension to feet.

Length:10 feet → 10.00 ft
Width:10 feet → 10.00 ft
Result: Length = 10.00 ft, Width = 10.00 ft
Step 2

Apply the rectangle formula A = L × W.

A = 10.00 × 10.00
Result: A = 100.00 sq ft
Final Answer
100.00

Worked Examples

See how the calculator works with different scenarios.

Scenario

The rectangle run on the values above, showing the full calculation path rather than only the answer.

Inputs

Shape:Rectangle
Unit:Feet
Quantity:1
Price:—

Calculation

1. Convert each dimension to feet. → Length = 10.00 ft, Width = 10.00 ft 2. Apply the rectangle formula A = L × W. → A = 100.00 sq ft

Result

100.00 sq ft

Interpretation

Order the net area plus the waste factor from the material plan — never the bare net figure.

Understanding Your Result

Your Result: Total area: 100.00 sq ft

Typical range: Bedroom 100–180 sq ft · living room 200–400 sq ft · 2-car garage ~400 sq ft · basketball court 4,700 sq ft · 1 acre 43,560 sq ft.

What This Means

Your rectangle measures 100.00 square feet — the two-dimensional space inside its boundary. That is the net figure: what you measure, not what you order.

Why It Matters

Square footage drives listing price, price-per-sq-ft comparisons, flooring and paint ordering, and tax assessment. Small measuring errors compound across large spaces, so modelling before buying is the cheapest form of due diligence.

Professional Interpretation

At 100.00 sq ft you need about 6 boxes of flooring (10% waste) or 115 tiles (15% waste). Keep one spare box or 5% spare tile for repairs.

How this is calculated

The area of a rectangle is its length multiplied by its width, both measured in the same unit.

What drives the result

Which shape is selected, the dimensions in a single consistent unit, and the quantity multiplier. Unit choice never changes the area — only the conversion factor applied first.

Recommendations

  • •Split irregular spaces into rectangles, triangles and circles and add the sections.
  • •Add waste before ordering: ×1.10 flooring, ×1.15 tile, ×1.20 diagonal tile.
  • •Measure twice — laser measurers beat tapes past ~20 ft.
  • •Keep spare material: dye lots change between batches.

Educational Content

Introduction

Square footage is area expressed in square feet — the 2-D space inside a boundary. In US real estate it drives listing price, price-per-sq-ft comparisons, flooring and paint ordering, and tax assessment. Appraisers call the official number Gross Living Area (GLA): finished, habitable, above-grade space.

Concept Explanation

One square foot is the area of a 1 ft × 1 ft square. Every shape reduces to that tile count: rectangles multiply sides, circles use πr², triangles halve base × height (or use Heron’s formula from three edges), and complex outlines split into pieces that are summed. Unit conversion always happens before the formula, so mixing feet and inches can never silently corrupt the result.

Applications

▸Flooring, tile, carpet and paint ordering with waste allowances
▸Real-estate listings, appraisals and price-per-sq-ft comparison
▸Concrete, sod, mulch and paver quantity takeoffs
▸HVAC sizing rules of thumb (e.g. ~20 BTU per sq ft cooling)
▸Roofing squares (1 square = 100 sq ft) and wall coverage

Benefits

  • •One calculator for 9 shapes — no separate tools per geometry
  • •Live diagram confirms you measured the right dimensions
  • •Material and cost plans generated from the same numbers
  • •Exact conversions to sq yd, sq m, sq in and acres

Limitations

  • •Flat-area geometry only — it does not add roof pitch or wall height
  • •Paint and wallpaper need wall area (perimeter × height), not floor area
  • •Appraisal GLA follows ANSI Z765 rules this tool does not enforce (ceiling height, egress, above-grade)

Best Practices

  • •Measure wall-to-wall for interiors, exterior-to-exterior for footprints
  • •Keep one unit throughout; convert inches to feet first
  • •Measure twice and photograph the tape for large jobs
  • •Add the trade waste factor before ordering, not after

Common Misconceptions

Myth: Square footage and floor area always mean the same thing.
Truth: Gross, net, rentable and GLA each include different spaces — garages and unfinished basements usually do not count.
Myth: You should order exactly the measured area.
Truth: Cuts, offcuts and breakage consume 10–20%. Ordering net guarantees a second trip.
Myth: A 12×12 room always needs 144 sq ft of material.
Truth: It needs about 160 sq ft of flooring (10% waste) or ~166 sq ft of tile (15% waste).

Practical Tips

  • •Use a preset room button to sanity-check your result before trusting site measurements.
  • •For L-shaped rooms, calculate two rectangles and add them — faster than any single formula.
  • •Take a photo of each measurement next to the tape for dispute-proof records.
  • •Enter your actual $/sq ft price to turn the area into a budget in one step.

Common Mistakes

Mixing feet and inches in one calculation.
Pick one unit in the dropdown — conversion is applied to every field automatically.
Ordering the net area with no waste allowance.
Use the material plan: ×1.10 flooring, ×1.15 tile, ×1.20 diagonal tile.
Measuring the wrong face of the wall.
Interiors are wall-to-wall; building footprints are exterior-to-exterior.
Counting garages and unfinished basements as living area.
Keep non-GLA spaces as separate runs so price-per-sq-ft math stays honest.
Single-coat paint math on a color change.
Most repaints need two coats — double the gallons from the material plan.

Assumptions

This calculator makes the following assumptions to provide estimates:

Flat plane: Area is measured on a flat plane; slope and pitch are not added.
Consistent unit: All inputs share the selected unit and are converted to feet once.
Euclidean geometry: Standard formulas; triangle edges must satisfy the triangle inequality.

Limitations

Be aware of these limitations when using this calculator:

Not an appraisal: GLA rules (ceiling height, egress, above-grade) are explained but not enforced.
Estimates, not quotes: Cost plans use allowances and your unit price — get 2–3 local quotes.

Frequently Asked Questions

Answers to common questions about this calculator.

What is square footage?
Square footage is a measurement of area expressed in square feet (sq ft or ft²) — the amount of two-dimensional space enclosed within a boundary. It is the standard unit for floor area in US real estate, construction and home improvement.
What is the difference between square footage and square feet?
There is no difference. “Square footage” is the common real-estate term; “square feet” (sq ft, ft²) is the technical unit.
How do you calculate square footage of a rectangle?
Multiply length × width in the same unit. A 12 ft × 12 ft room is 144 sq ft.
How do you calculate square footage with feet and inches?
Convert inches to feet (divide by 12), then multiply. Example: 12 ft 6 in × 10 ft 3 in = 12.5 × 10.25 = 128.13 sq ft. Select “Inches” as the unit above and the conversion is automatic.
How do I calculate a circle’s square footage?
A = π × r² where r is half the diameter. A 6-ft-diameter table is π × 3² ≈ 28.27 sq ft.
How do I calculate a triangle when only 3 sides are known?
Use Heron’s formula: s = (a+b+c)/2, then A = √(s(s−a)(s−b)(s−c)). Choose “Triangle (Edges)” above and it is done automatically.
How do I calculate a trapezoid?
A = ½ × (base₁ + base₂) × height. Example: bases 10 and 14 ft with 8 ft height = 96 sq ft.
How do I calculate a ring (annulus)?
Outer circle area minus inner circle area: πR² − πr². Enter the outer diameter and border width and the calculator handles it.
How many square feet are in an acre?
43,560 sq ft per acre (≈ 4,046.9 m², 0.4047 ha).
How do I convert square feet to square yards?
Divide by 9. Example: 300 sq ft ÷ 9 = 33.33 sq yd. The results dashboard shows every conversion live.
How many square feet is a 12×12 room? A 20×20 room?
12×12 = 144 sq ft (typical bedroom). 20×20 = 400 sq ft (master bedroom or small studio). Try the preset buttons above the form.
How do I measure an irregular room?
Split it into rectangles, triangles and circles, calculate each section, then add them up. Use the Quantity field for repeated rooms, or run the calculator once per section and sum the results.
Do closets and hallways count in square footage?
In listings, finished habitable closets and hallways count toward Gross Living Area (GLA). Garages, unfinished basements, porches and decks do not. See the ANSI Z765 notes in the education section.
How do I estimate paint from square footage?
Wall area = room perimeter × wall height, minus ~15 sq ft per window and ~20 sq ft per door. One gallon covers 350–400 sq ft per coat. A 12×12 room with 8-ft ceilings needs about 1 gallon per coat.
How much flooring do I order for my square footage?
Order the net area plus a waste allowance: 10% for laminate, vinyl and carpet, 15% for tile (20% for diagonal layouts). The material plan below computes boxes and tiles for you.
What does square footage cost to build or finish?
US 2026 benchmarks: laminate $1–5, vinyl $2–7, hardwood $5–15, tile $7–25 and interior paint $2–6 per sq ft; new residential construction $100–400+ per sq ft. Enter any unit price above for a live total.
What is Gross Living Area (GLA)?
The appraiser’s term for finished, habitable, above-grade area: bedrooms, baths, kitchen, living areas and qualifying finished basements/attics. Excludes garages, unfinished space, porches, patios and decks.
Gross vs net vs rentable square feet?
Gross (GSF) is everything inside the exterior walls. Net/usable (NSF/USF) is space you actually occupy. Rentable (RSF) is usable plus your share of common areas — the number commercial rent is charged on.
How accurate is this square footage calculator?
Every figure follows directly from the inputs using standard geometry, so it is accurate to the quality of your measurements. Measure twice, keep one unit throughout, and verify on site before ordering materials.

Related Calculators

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Related Guides

Deepen your understanding with these educational resources.

Glossary

Technical terms used in mortgage calculations explained in plain language.

Square foot (sq ft, ft²)
Area of a 1 ft × 1 ft square. 144 sq in = 1 sq ft; 9 sq ft = 1 sq yd.
Gross Living Area (GLA)
Finished, habitable, above-grade residential area measured per ANSI Z765.
GSF / NSF
Gross square feet (whole building incl. walls and mechanical) vs net square feet (usable tenant space).
RSF / USF
Commercial terms: rentable SF (incl. share of common areas) vs usable SF (actually occupied). The load factor converts USF to RSF.
FAR
Floor Area Ratio: total building floor area divided by lot area — a zoning density control.
Waste factor
Extra material ordered for cuts, offcuts and errors — typically 10% for flooring, 15–20% for tile and diagonal layouts.
Takeoff
Measuring quantities from plans or dimensions to build the material shopping list.
A roofing “square”
100 sq ft of roof area — the trade unit for shingles and roofing cost.

Authoritative References

Trusted sources and standards referenced by this calculator.

Applicable Standards

ANSI Z765: measure residential area to the nearest 1/10 ft, above-grade finished space onlyIRC R305: habitable rooms need ≥ 7 ft ceilings to qualify as living areaIRC R310: basement bedrooms need egress windows or doors to count as bedrooms1 acre = 43,560 sq ft · 1 sq yd = 9 sq ft · 1 sq m ≈ 10.764 sq ftMoney rounded for display only; all calculations run at full precision

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Page Information

Last Updated:

2026-09-23

Version:

2.0.0

License:

Free to use for educational and professional purposes.