How to Measure Square Footage of a House (Room-by-Room Method)

Whether you’re estimating a remodel, listing a home, or just trying to figure out how much flooring to order, you need accurate square footage. And after 20 years of measuring houses for bids, I can tell you this: the number you find online, the number on the tax record, and the number you actually measure are rarely the same.

The room-by-room method I use on every project is simple, accurate, and works on any house layout. No special equipment needed, just a tape measure, a notepad, and about 30 minutes.

This guide covers how to measure each room, handle irregular shapes, understand what actually counts as livable square footage, and avoid the mistakes I see constantly.

The Room-by-Room Method

This is how professionals do it. You measure each room individually, then add them all together. It sounds tedious, but it’s the most accurate approach, especially for older homes where nothing is perfectly square.

What You Need

Tape measure (25-foot minimum, 35-foot is better for large rooms)
Paper and pen or your phone’s notes app
A helper (makes long measurements much easier, but not required)
A simple floor plan sketch (doesn’t have to be pretty, just a rough layout so you don’t miss rooms)

Step 1: Sketch the Floor Plan

Walk through the house and draw a rough outline of every room on each floor. Label them: living room, bedroom 1, kitchen, hallway, etc. Include closets. This sketch is your checklist so you don’t accidentally skip a space.

Step 2: Measure Each Room

For each room, measure the length and width in feet. Measure wall to wall at floor level. Don’t measure to the baseboard, measure to the wall behind it.

Rectangular rooms: Length x Width = Square Feet

Living room: 18 ft x 14 ft = 252 SF
Bedroom 1: 12 ft x 11 ft = 132 SF
Kitchen: 15 ft x 12 ft = 180 SF

Round to the nearest inch, then convert to decimal feet for multiplication:

6 inches = 0.5 ft
3 inches = 0.25 ft
9 inches = 0.75 ft

So a room that measures 12 feet 6 inches by 10 feet 3 inches is 12.5 x 10.25 = 128.1 SF.

Step 3: Handle Hallways

Hallways are easy to forget, but they add up fast. A typical hallway (3.5 feet wide by 15 feet long) is 52.5 square feet. In a house with multiple hallways, you can easily have 150-200 SF of hallway space.

Measure each hallway as its own rectangle: width x length.

Step 4: Measure Closets

Walk-in closets and standard closets both count toward livable square footage. Measure them the same way: width x depth.

A standard closet (2 ft x 5 ft) adds 10 SF. A walk-in (6 ft x 8 ft) adds 48 SF. Don’t skip these. In a 3-bedroom house, closets can easily total 100+ SF.

Step 5: Add It All Up

Sum every room, hallway, and closet on each floor. Then add the floors together for total square footage.

Pro tip: Use our square footage calculator to do the math as you go. Punch in each room’s dimensions and let it track the running total. It’s faster than doing it by hand, especially when you’re measuring 15+ spaces.

Handling Irregular Shapes

Not every room is a perfect rectangle. Here’s how to handle the common ones.

L-Shaped Rooms

Break the L into two rectangles. Measure each one separately and add them together.

Example: An L-shaped living room

Section A: 18 ft x 12 ft = 216 SF
Section B: 8 ft x 10 ft = 80 SF
Total: 296 SF

Rooms with Bay Windows or Bump-Outs

Measure the main rectangle of the room first, then measure the bump-out separately and add it.

Example: A bedroom with a bay window

Main room: 14 ft x 12 ft = 168 SF
Bay window bump-out: 6 ft x 3 ft = 18 SF
Total: 186 SF

Rooms with Angles or Cutoffs

For rooms with angled walls (common in older homes or rooms under rooflines), break the space into a rectangle plus a triangle.

Triangle formula: (Base x Height) / 2

Example: A room that’s 12 ft wide, 14 ft on the long side, and has a 45-degree angle cutting off one corner (4 ft x 4 ft triangle).

Full rectangle: 12 x 14 = 168 SF
Subtract the triangle: (4 x 4) / 2 = 8 SF
Total: 160 SF

Rooms with Curves (Turrets, Round Alcoves)

For curved walls, measure as if the wall were straight (use the widest point) and you’ll be close enough for estimating purposes. For exact calculations, you’d need the radius and the arc formula, but for material ordering or general square footage, the straight-line approximation works.

What Counts as Livable Square Footage

This is where it gets confusing, because the rules depend on who’s measuring and why.

Included in Livable Square Footage

All finished rooms on above-grade (above ground) floors
Hallways, closets, and landings
Finished attic space with ceiling height of 7 feet or more
Second and third floors
Enclosed, heated porches or sunrooms

NOT Included in Livable Square Footage

Garages (attached or detached)
Unfinished basements (even if you use them)
Unfinished attics
Open porches, decks, and patios
Covered but unenclosed spaces (carports, covered patios)
Areas with ceiling height under 5 feet (under sloped roofs)

The Gray Areas

Finished basements: Some appraisers count them, some don’t. Even when counted, they’re often listed separately as “below-grade finished square footage.” For real estate purposes, a finished basement usually adds value but isn’t included in the main square footage number.
Enclosed porches: If it’s heated and has the same finish quality as the rest of the house, most appraisers include it. If it’s a three-season porch with different flooring and no heat, probably not.
Loft spaces: If the ceiling is over 7 feet and the space is accessible by permanent stairs (not a ladder), it typically counts.

Why Different Numbers Exist for the Same House

If you’ve ever noticed that the county tax record, the real estate listing, and your tape measure all give different numbers, here’s why.

Tax Records (County Assessor)

Often based on original building permits and may not reflect additions, remodels, or finished spaces added later. I’ve seen tax records that are off by hundreds of square feet because the homeowner finished a basement or added a room without pulling a permit.

Real Estate Listings (MLS)

The listing agent typically uses the appraiser’s number, the builder’s number, or their own measurement. There’s no universal standard for how agents measure, and some are more careful than others. ANSI standards exist but aren’t required in every state.

Builder’s Plans

These show the design dimensions, not the as-built dimensions. Walls might be framed slightly differently, bump-outs might change during construction, and the plans don’t account for the actual finished wall-to-wall measurements.

Your Tape Measure

This is the most accurate for your purposes. You’re measuring the actual space as it exists today. For material ordering, remodel bidding, or personal knowledge, your measurement is the one that matters.

Common Mistakes When Measuring Square Footage

Mistake 1: Measuring Exterior Walls Instead of Interior

For livable square footage, you measure wall to wall inside the house. Exterior dimensions include the wall thickness (typically 4-6 inches on each side), which adds significant area that isn’t livable space. On a 2,000 SF house, exterior measurements might read 2,200+ SF.

Mistake 2: Forgetting to Subtract Interior Walls

When you measure room by room, this handles itself automatically. But if you’re measuring the whole floor as one big rectangle and subtracting, don’t forget that interior walls take up space too.

Mistake 3: Including the Garage

The garage is not livable space. Even if it’s heated. Even if it’s been converted to a workshop. Unless it’s been formally converted to living space with permits and proper finishing, don’t count it.

Mistake 4: Counting Stairways Twice

Stairs connect two floors. Count the footprint of the stairway on each floor only once. The upper floor opening (the stair well) is not usable floor space on that level.

Mistake 5: Skipping Small Spaces

Hallways, closets, pantries, laundry rooms, and nooks all count. In a typical house, these “small” spaces add up to 200-400 SF. Skipping them means your total is significantly under the actual square footage.

Using Square Footage for Material Estimates

Once you have your square footage, here’s how it connects to common project estimates:

Flooring: Your square footage is the starting point, but you’ll add waste factor by material type. Use our flooring calculator to add the right waste percentage.
Paint: One gallon covers about 350-400 SF of wall area. But wall area isn’t the same as floor area. You need to measure wall height and perimeter for paint. Our paint calculator handles this conversion.
General remodel budgets: Many contractors price remodels by the square foot as a rough starting point. Knowing your accurate square footage helps you evaluate whether a bid is in the right ballpark.

Frequently Asked Questions

How do I calculate square footage from outside measurements?

Measure the exterior length and width, then subtract the wall thickness from each side. For standard wood-frame construction, subtract about 1 foot from each dimension (6 inches per wall). For brick or stone, subtract about 1.5 feet per dimension. This gives you a rough interior figure, but measuring inside is always more accurate.

Do I include the basement in square footage?

Only if it’s finished and you’re noting it separately. For standard livable square footage (the number used in real estate listings), unfinished basements don’t count. Finished basements are typically listed as “below-grade finished area” separately from the main square footage.

How accurate do I need to be for ordering materials?

Within 5% is solid for most material orders. You’ll add waste factor on top of your measurement anyway (10% for flooring, 15% for tile, etc.), so being off by a few square feet per room won’t cause problems. Being off by 100 SF across the whole house will, which is why room-by-room measuring beats eyeballing.

Is there an app that measures square footage?

There are laser measuring tools and phone apps that use AR to measure rooms. They’re getting better, but I still use a tape measure for anything that matters. The technology is convenient for quick estimates, not reliable enough for ordering materials or writing bids.

How do I measure a room with a vaulted ceiling?

Ceiling height doesn’t affect square footage. Square footage is a floor measurement. A room with a vaulted ceiling has the same square footage as the same room with a flat 8-foot ceiling. Ceiling height only matters when calculating wall area for paint or wallpaper.

Measure Once, Measure Right

Accurate square footage is the foundation of every material estimate, project bid, and space planning decision. The room-by-room method takes 30 minutes and gives you a number you can trust, which is more than you can say about the county tax record or the old real estate listing.

Grab a tape measure, sketch your floor plan, and work room by room. Use our square footage calculator to keep a running total as you go. And if you’re measuring for a specific project like flooring or paint, jump straight to the project-specific calculators that factor in waste and coverage rates.

If you need a refresher on measuring individual rooms before tackling a full house, how to measure square footage covers rectangular rooms, L-shapes, and the most common measuring mistakes. For a detailed walkthrough of how to apply your square footage measurements to a flooring order with proper waste factors, see our guide on square footage for flooring. For a step-by-step ordering guide with waste factors by material type, see square footage for flooring: how to calculate and order the right amount. And if you’re an estimator or contractor turning these measurements into a bid, how to estimate construction jobs covers the full process.

Brad is a third-generation contractor with over 20 years of experience in residential remodeling. He’s the founder of EstimationPro.AI, helping contractors and homeowners estimate projects accurately.