Square Footage & Floor Area Calculator (m², ft², pyeong)

Understanding the square footage calculator — concept and principle

This calculator adds up the floor area of a room or a whole home from its rectangles, plus an optional round area, and shows the total in square metres, square feet, square yards and Korean pyeong. Use it when buying flooring or paint, comparing listings, or converting a Korean apartment size to an international unit.

How it is calculated

Area of each rectangle = length × width

Round area = π × diameter² ÷ 4

Total = sum of rectangles + round area

• Each line of the input is one rectangle written as "length x width". Split an L-shaped room into two rectangles that do not overlap.
• Lengths are converted to metres first: 1 ft = 0.3048 m exactly, 1 cm = 0.01 m.
• Conversions: 1 ft² = 0.09290304 m², 1 yd² = 0.83612736 m², 1 pyeong = 400/121 m² ≈ 3.3058 m².
• The page also shows how many rectangles were counted and the largest one.

The principle

Area is additive: if a shape can be cut into pieces that do not overlap, its area equals the sum of the pieces. That is why any room with straight walls and right angles can be measured as a set of rectangles. A rectangle's area is length times width because it holds that many unit squares. Unit conversions square the length factor: since a foot is 0.3048 m, a square foot is 0.3048² = 0.09290304 m². The pyeong comes from the traditional unit of 6 × 6 ja, with 1 ja = 10/33 m, so 1 pyeong = (60/33)² = 400/121 m².

Worked example

Default inputs: metres, rectangles 4.2 x 3.6 and 3 x 2.4, no round area.

1. First rectangle = 4.2 × 3.6 = 15.12 m² (the largest).
2. Second rectangle = 3 × 2.4 = 7.2 m².
3. Total = 15.12 + 7.2 = 22.32 m², from 2 rectangles.
4. In square feet: 22.32 ÷ 0.09290304 = 240.25 ft².
5. In pyeong: 22.32 × 121 ÷ 400 = 6.75 pyeong; in square yards: 22.32 ÷ 0.83612736 = 26.69 yd².

How to read the result

The total is the net floor area you measured. For flooring, add a waste allowance, often 5–10 % for straight laying and more for diagonal patterns. When you compare homes, check which area a listing uses: Korean listings often quote supply area (공급면적), which includes a share of shared spaces, while exclusive area (전용면적) is the unit's own floor. A bedroom of about 10 m² is roughly 3 pyeong or 108 ft².

Common mistakes

• Overlapping rectangles when splitting an L-shaped room, which counts a corner twice.
• Mixing units, such as metres for one wall and centimetres for another.
• Converting square metres to square feet with 3.28 instead of 3.28² (about 10.76).
• Comparing a supply area with an exclusive area.

Frequently asked questions

How many square feet is one pyeong?

About 35.58 ft², since 1 pyeong ≈ 3.3058 m².

How do I measure an irregular room?

Split it into rectangles and, for a curved bay, a circle or semicircle. A semicircle is half the round area for its diameter.

Do I include closets?

For flooring, yes if they get the same floor. For listings, follow the rule the listing uses.

Sources: NIST Special Publication 811, Guide for the Use of the International System of Units (1 ft = 0.3048 m) · Definition of the pyeong as 6 × 6 ja with 1 ja = 10/33 m (400/121 m²)