Square Footage Calculator

Q: What's the formula for a ring's area?

π × (R² − r²), outer radius R, inner radius r. Same as the area of the outer circle minus the area of the inner circle.

Q: How do I get area from three sides of a triangle?

Heron's formula: semi-perimeter s = (a + b + c) / 2, then area = √[s(s−a)(s−b)(s−c)]. The three sides have to form a valid triangle (any two sides must add up to more than the third). We check that for you here.

Q: What's the difference between area and surface area?

Area is the size of a flat 2D shape (floor, wall, lot). Surface area is the total of all faces on a 3D object (box, ball). This tool does 2D area; for 3D you'd add up each face.

Q: How do I calculate the area of a sector?

Sector (pie slice): (θ/360) × πr² for area, (θ/360) × 2πr for the curved arc length. θ is the angle in degrees, r is the radius. We show both.

Q: What's the formula for parallelogram area?

A = b × h, base times perpendicular height (not the slanted side). Same as a rectangle: a parallelogram can be cut and rearranged into one.

Square Footage Calculator: Area of Rectangle, Circle, Triangle & More

Free square footage calculator for nine shapes. Area, perimeter, and arc length in feet, meters, or any unit, conversions update as you go.

What This Square Footage Calculator Does

This square footage calculator computes area and perimeter for nine common shapes: rectangle, rectangle border (hollow), parallelogram, trapezoid, circle, ring (annulus), sector (pie slice), and two triangle modes (base-height and Heron's three-side formula). Select a shape, choose a measurement unit (feet, meters, inches, yards, or others), and enter dimensions. The calculator applies the correct formula for each shape, validates inputs (e.g., triangle inequality for Heron's), and returns area in square units plus perimeter or circumference. It does not calculate surface area for 3D objects or handle irregular polygons, break those into simpler shapes and sum the results.

How to Use This Calculator

Select a shape, choose your measurement unit, and enter the required dimensions to get area and perimeter instantly.

Shape Selector:

Choose from nine shapes: rectangle, rectangle border, parallelogram, trapezoid, circle, ring, sector, or triangle (base-height or three-side Heron mode).
Unit:

Select feet, meters, inches, yards, or another unit. All input fields and results convert automatically, no manual conversion needed.
Dimensions:

Fill in the required measurements for your chosen shape. A labeled diagram shows exactly which dimension goes where.
Results:

Area in square units, perimeter or circumference, and arc length for sectors. Ready for flooring, paint, landscaping, or material ordering.

Area vs. surface area

2D vs 3D

Area is for flat shapes; surface area is for 3D objects.

Area (2D):

Floors, walls, lawns, patios, any flat surface. We do this here.
Surface area (3D):

Every face of a box, ball, or cylinder. You have to find each face and add them up.

Formulas at a glance

Rectangle:

A = L × W
L length, W width.
Rectangle border (hollow):

A = (L_outer × W_outer) − (L_inner × W_inner)
Outer minus inner rectangle.
Parallelogram:

A = b × h
Base × perpendicular height. Same as rectangle (parallelogram can be rearranged into one).
Trapezoid:

A = ½(a + b) × h
a, b parallel bases; h height.
Circle:

A = πr²
Circumference C = 2πr.
Ring (annulus):

A = π(R² − r²)
R outer, r inner radius.
Sector (pie slice):

A = (θ/360) × πr²
Arc length (θ/360) × 2πr. θ in degrees.
Triangle (base × height):

A = ½b × h
Perpendicular height.
Triangle (Heron):

s = (a+b+c)/2
A = √[s(s−a)(s−b)(s−c)]
Sides a, b, c. Need: any two sides sum > third.

Where you'll use it

Common uses

Flooring and carpet:

Get square footage, then add 5–10% for cuts and waste.
Paint:

Wall area for coverage. Most paint is 350–400 sq ft per gallon, check the can.
Landscaping:

Beds, patios, paths. Use circles and sectors for curves; add shapes together for odd layouts.
Ordering materials:

Suppliers use sq ft, sq yd, or sq m. Convert once you have your area.

FAQ

How do I calculate the area of an L-shaped room?

Split it into two rectangles, find each area (length × width), then add them. Example: 10 ft × 8 ft = 80 sq ft and 6 ft × 4 ft = 24 sq ft → 104 sq ft total.

What's the formula for a ring's area?

π × (R² − r²), outer radius R, inner radius r. Same as the area of the outer circle minus the area of the inner circle.

How do I get area from three sides of a triangle?

Heron's formula: semi-perimeter s = (a + b + c) / 2, then area = √[s(s−a)(s−b)(s−c)]. The three sides have to form a valid triangle (any two sides must add up to more than the third). We check that for you here.

What's the difference between area and surface area?

Area is the size of a flat 2D shape (floor, wall, lot). Surface area is the total of all faces on a 3D object (box, ball). This tool does 2D area; for 3D you'd add up each face.

How do I calculate the area of a sector?

Sector (pie slice): (θ/360) × πr² for area, (θ/360) × 2πr for the curved arc length. θ is the angle in degrees, r is the radius. We show both.

What's the formula for parallelogram area?

A = b × h, base times perpendicular height (not the slanted side). Same as a rectangle: a parallelogram can be cut and rearranged into one.

Shape & dimensions

Cost estimator

Square Footage Calculator: Area, Perimeter & Units

What this calculator does

Nine shapes

One unit, all inputs

Perimeter and arc length

Labeled diagrams