Square Footage Calculator
Compute area for rectangles, circles, and triangles — or solve a missing dimension from a known area.
Calculation Steps
Practical Guide
Square Footage Calculator: Measure Rooms, Areas, and Projects the Right Way
This hands-on guide mirrors the calculator above so you can quickly measure rooms, combine shapes, subtract openings, and convert units. We’ll cover the fastest methods, what drives mistakes, and worked examples in US/metric with clear rounding rules.
Quick Start
- 1 In Solve for, choose Area (ft², yd², m²) or Side if you’re working backwards from an area target.
- 2 Select a shape mode: Rectangle, Circle, Triangle, Trapezoid, or Composite (sum of shapes). For L-shapes, split into two rectangles.
- 3 Enter dimensions and units. For rectangles use \(L\) and \(W\); for circles use radius or diameter.
- 4 Use the Subtractions inputs to remove stairs, fireplaces, or uncounted niches for a net area.
- 5 Review the result and convert to yd² or m² as needed. Round to your trade’s convention (e.g., flooring often rounds up to the nearest box/roll).
Tip: Measure to the nearest inch (or centimeter) and keep units consistent end-to-end. Small rounding errors multiply when you add many rooms.
Watch-out: Don’t confuse linear feet (length) with square feet (area). If you only have perimeter, you still need an average width to estimate area.
Variables & Symbols
- \(A\) Area (ft², yd², m²)
- \(L\) Length
- \(W\) Width
- \(r\) Circle radius; \(d=2r\)
- \(b\) Triangle base
- \(h\) Height (triangle/trapezoid)
- \(a,b\) Trapezoid parallel sides
Choosing Your Method
Method A — Room by Shape
Best for most rooms and simple outdoor spaces.
- Fast: measure \(L\) and \(W\) or radius/diameter.
- Easy to audit and re-measure if needed.
- Matches how most material quotes are built.
- Irregular rooms need splitting into multiple shapes.
- Angles/curves can be approximated unless you capture arcs.
Method B — Composite / Takeoff
Ideal for L-shapes, open plans, or plan sets.
- Accurate for complex footprints when you decompose into parts.
- Lets you subtract stairs, chimneys, or voids for net area.
- Takes a little more time and organization.
- Requires a consistent measurement convention across rooms.
What Moves the Number the Most
Mixing inches with feet (or cm with m) causes 8–12% swings fast. Convert first, then calculate.
Inside vs outside of trim, wall bowing, and alcoves all change totals. Pick a convention and stick to it.
Large openings (stair voids, double-height spaces) should be removed for net square footage used in material estimates.
Flooring often rounds up to the next carton or full yard; countertops and turf may round to cuttable widths.
Approximating curves as rectangles inflates totals; conversely, forgetting niches undercounts.
For roofs or slopes, plan on surface area (not plan area) and include lap/coverage factors by product.
Worked Examples
Example 1 — US Imperial: L-Shaped Room (Two Rectangles)
- Space: L-shaped living/dining area
- Part A: 16 ft × 12 ft
- Part B: 10 ft × 8 ft
- Subtraction: Fireplace hearth 2 ft × 3 ft
- Output: Net ft² and yd²
For flooring, round up to the nearest box or add a small waste factor (typically 5–10% for plank/tile layout).
Example 2 — Metric: Mixed Shapes (Rectangle + Half-Circle)
- Patio: 5.0 m × 4.0 m rectangle with a semicircle (radius 2.0 m) on one long side
- Subtractions: None
- Output: m² and ft²
When mixing shapes, compute each piece in the same units first, then convert once at the end.
Shapes, Conversions & Variations
Use the table to check formulas, common conversions, and where rounding rules differ across trades.
| Item | Formula / Conversion | Notes |
|---|---|---|
| Rectangle | \(A = L \times W\) | Fastest for most rooms; measure to drywall or finished trim consistently. |
| Triangle | \(A=\dfrac{b \times h}{2}\) | Use perpendicular height to base; for right triangles \(b\) and \(h\) are the legs. |
| Circle | \(A=\pi r^2=\pi(d/2)^2\) | Measure radius to the center; for arcs use sector fraction × \(\pi r^2\). |
| Trapezoid | \(A=\dfrac{(a+b)}{2}h\) | Great for tapered yards and driveways. |
| Square yards | \( \text{yd}^2 = \dfrac{\text{ft}^2}{9}\) | Carpet and turf are often priced in yd²—round up to roll width. |
| Square meters | \(\text{m}^2 = \text{ft}^2 \times 0.092903\) | Metric building plans typically dimension in millimeters; convert before calculating. |
| Acres | \(\text{acres} = \dfrac{\text{ft}^2}{43{,}560} = \dfrac{\text{m}^2}{4046.856}\) | Useful for lots and large landscaping takeoffs. |
| Roof “squares” | \(\text{squares} = \dfrac{\text{ft}^2}{100}\) | Use sloped surface area (pitch factor), not plan area, and include shingle overlap. |
- Convert all dimensions to the same unit before multiplying.
- Subtract significant voids for net area used in materials.
- Document assumptions (inside vs outside trim, rounding).
- Save your inputs—future changes go 10× faster with a record.
- For roofs, apply a pitch factor to get true surface area.
- When ordering, align rounding with vendor pack sizes.
Using the Result & Sanity Checks
Material Planning
- Flooring: Convert to yd²/m² and add 5–10% for cuts/patterns; more for diagonal or herringbone layouts.
- Paint: Multiply wall area by coats and coverage (ft²/gal or m²/L) after subtracting large openings.
- Concrete/asphalt: Area × thickness gives volume; be sure thickness is in the same base units.
Documentation
- Record measurement points (centerline vs finished face).
- Include a sketch with shape splits and dimensions.
- Note date, device, and any laser/tape calibration details.
Sanity Checks
- Does the total align with room photos and feel “about right” (e.g., a 12×12 is ~144 ft²)?
- Cross-check using an alternate split (two rectangles vs one + subtractions).
- If converting to yd² or m², recompute back to ft² to confirm math.
Real-estate reporting standards (e.g., what counts as gross living area) vary. For contracts or appraisals, follow the applicable standard and local rules.