Square Foot Calculator House: How to Measure Any Home

This square footage calculator works out the total floor area of a house or individual room. You enter the length and width of each rectangular section in feet (or meters), and it returns the area in square feet (or square meters) and adds the sections together for a whole-home total. It uses the standard formula: area = length × width, applied to each room or floor section.

Formula

The formula for a single rectangular section is:

Area = Length × Width

Where:

• Length (l) is the longer dimension of the room or section, in feet (or meters).
• Width (w) is the shorter dimension, in the same unit.
• Area is the floor area, in square feet (sq ft) or square meters (m²).

For a whole house, you sum the areas of all individual sections:

Total Area = (l₁ × w₁) + (l₂ × w₂) + … + (lₙ × wₙ)

Worked Example

Using the default values from the calculator: a room that is 30 feet long and 20 feet wide, with 1 section.

1. Multiply length by width: 30 × 20 = 600
2. The area per section is 600 square feet.
3. Multiply by the number of sections (1): 600 × 1 = 600
4. The total area is 600 square feet.

That matches the calculator’s output of 600.0 sq ft.

Why Measure Square Footage?

Square footage is the standard way to describe house size in the United States and Canada. It affects property listings, property taxes, insurance premiums, and how much paint or flooring you need to buy. Even if you are not selling, knowing your home’s area helps you plan renovations, compare rentals, or estimate heating and cooling loads.

In most of the world, the same measurement is done in square meters. One square foot equals 0.0929 square meters, so to convert, multiply square feet by 0.0929. To go the other way, multiply square meters by 10.764.

How to Measure a House Step by Step

1. Draw a sketch of each floor, breaking it into rectangles. You can measure the outside of the house for gross living area, or the inside for usable floor area.
2. Measure each rectangle with a tape measure or laser measure. For the outside, measure from the exterior walls. For the inside, measure from wall to wall.
3. Multiply length × width for each rectangle.
4. Add all the areas together to get the total.
5. Subtract areas that are not living space (if you are calculating “gross living area”): garages, porches, balconies, and unfinished basements are usually excluded.

Common Mistakes and Misconceptions

• Mixing units: Always use the same unit for length and width. If you measure one side in feet and the other in inches, convert first (12 inches = 1 foot).
• Including non-living spaces: For a real estate listing, you typically count only finished, heated living space. A garage or an unfinished basement is not counted.
• Measuring at floor level vs. wall level: For accuracy, measure at the floor, but if baseboards are thick, measure from wall to wall, not from baseboard to baseboard.
• Rounding too early: Round only at the end. If you round each room to the nearest foot, you can lose accuracy across many rooms.
• Assuming the house is a perfect rectangle: Most homes have alcoves, bay windows, or irregular shapes. Break them into smaller rectangles and add them up.

How to Use the Calculator for Irregular Rooms

For an L-shaped room, divide it into two rectangles. Measure each rectangle separately, then add the two areas. For a triangular section, use the formula: area = (base × height) / 2. The calculator above works for rectangles; for triangles, you can compute the area manually and then add it to the total from the calculator.

For a circular room (rare but possible), use the formula: area = π × radius². The calculator does not handle circles directly, but you can compute the area separately and add it.

What Counts as Living Space?

Definitions vary by locality and by appraisal standards, but generally, “gross living area” (GLA) includes:

• Finished, heated, and cooled rooms above grade (bedrooms, living rooms, kitchens, finished basements if they meet local codes).
• Staircases (counted once, usually on the floor they start from).
• Hallways and closets.

Excluded are:

• Unfinished basements or attics.
• Garages, carports, and sheds.
• Porches, balconies, and decks (unless enclosed and heated).
• Common areas in condos (like hallways) if you own only the unit.

Always check with a local appraiser or real estate agent if the exact definition matters for a sale.

Square Feet vs. Square Meters

If you measure in meters, the calculator gives square meters. If you need square feet, multiply the square meters by 10.764. Conversely, multiply square feet by 0.0929 to get square meters. For example, a 100 m² apartment is about 1,076 sq ft.

Frequently Asked Questions

How do I calculate the square footage of a house with multiple floors?

Measure each floor separately using the same method, then add the totals together. For example, if the first floor is 1,200 sq ft and the second floor is 1,000 sq ft, the total is 2,200 sq ft. Do not double-count staircases: usually they are counted once, on the floor where they begin.

Does the calculator include walls?

No, it calculates the area inside the length and width you enter. If you measure the exterior dimensions, you get the gross area including wall thickness. For interior living space, measure from interior wall to interior wall. Most real estate listings use the exterior dimensions for the “house size,” but the difference is usually small.

How do I measure a room that is not a perfect rectangle?

Divide the room into rectangles. Measure each rectangle’s length and width, compute each area, and add them together. For a triangular part, use (base × height) / 2. For a circular part, use π × radius². Add all parts to get the total.

What is the difference between square footage and square meters?

They are two units for the same quantity: area. One square foot is 0.0929 square meters, and one square meter is 10.764 square feet. To convert, multiply by the appropriate factor. For example, 2,000 sq ft = 2,000 × 0.0929 = 185.8 m².

Should I include a garage in the square footage?

Usually no, unless it is finished and heated and meets local living-space requirements. Most appraisal standards exclude garages, carports, and unheated spaces. If you are listing your home, ask your real estate agent what the local convention is.

Why does my property tax record show a different square footage than my own measurement?

Tax records often use exterior dimensions and may include or exclude certain areas differently. They may also be outdated if you have finished a basement or added a room. Your own measurement is more accurate for renovations, but for tax purposes, the official record is what matters.

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in l | Length | ft | 30 | 0
in w | Width | ft | 20 | 0
in sections | Number of sections | - | 1 | 1
out area | Area per section | sq ft | l * w | 1
out total | Total area | sq ft | (l * w) * sections | 1