The short answer
Quick answer
Break the floor into rectangles, multiply length by width in feet for each one, add them together, then add the closets and doorways. After that you add waste. Waste isn't a flat 10 percent for everything. It runs about 5 to 10 percent for a straight-lay plank floor, roughly 15 percent on a diagonal, and 20 percent or more for herringbone or a patterned tile floor.
Search this question and you get calculators. Length times width, add ten percent, done. That math is right. It's just not the part that decides your order. What changes your order is everything the calculator doesn't ask: the closets, the doorways, the wall that isn't parallel to the one across from it, and the fact that carpet doesn't come in square feet at all.
Here's how we do it across Alexandria, Arlington, Fairfax and the rest of the DMV, and where homeowners' numbers usually go wrong.
What you need
Quick answer
A 25-foot tape, paper or your phone's notes, and a calculator. A laser measure is faster and fine for open rooms, but it reads to whatever it hits, so a curtain or a stack of boxes gives you a short wall.
Sketch the room first, roughly to shape, before you measure anything. Every number you take goes on the sketch next to the wall it came from. If you measure first and write later you'll transpose two of them, and you won't know which two.
Measure at floor level, along the baseboard. Walls lean, and a number taken at waist height in a house that's settled can be off by half an inch over a long run. Half an inch doesn't matter on one wall. It matters when you've made the same mistake in six rooms.
Break the floor into rectangles
Quick answer
Anything that isn't a plain box gets split into boxes. An L-shaped family room is two rectangles. A room with a bay window is a rectangle plus a small one. Measure each, multiply each, add them up.
This is the whole method and it handles every shape you'll meet in a house. Draw a line across your sketch where the shape changes, label the two pieces A and B, and treat them as separate rooms that happen to share a line.
Angles and curves get squared off. A bay window with three faces gets measured as the rectangle it sits inside, and you eat the small overage. Nobody orders flooring to a triangle, and the offcut from an angled wall is waste either way.
💡 Key takeaway
Keep every room on its own line in your notes, with its own total. One combined number is useless later. When a quote comes back higher than you expected, per-room numbers tell you which room did it.
Measure in inches, then convert once
Quick answer
Write measurements as feet and inches, then divide the inches by 12 to get a decimal foot. A room 12 feet 7 inches long is 12.58 feet, not 12.7. We see it on homeowners' own numbers all the time.
Seven inches is seven twelfths of a foot, which is 0.58. Writing it as 12.7 overstates that wall by about an inch and a half. Do it in every room on a 1,500 square foot main level and you're paying for material you don't need, on a product you can't return once the boxes are open. The same mistake in the other direction, writing 12 feet 7 as a flat 12, leaves you short. Short means a second order, a second delivery, and possibly a different production run of the same product.
Round up, never down. If the tape reads a hair over 12 feet 7, call it 12 feet 8. You want the error on the side of having a spare plank.
Closets, doorways and thresholds
Quick answer
Measure every closet as its own little rectangle and add it. Add the pocket of floor inside each doorway too, where the flooring runs through the jamb to the middle of the threshold. Both get missed constantly.
A reach-in closet is easy to forget because you don't stand in it. It's still floor, it still gets planks, and a 4-foot by 5-foot closet is 20 square feet. Miss three of them in a house and you're 60 square feet short.
Doorways are smaller and sneakier. The flooring doesn't stop at the face of the wall, it runs into the door opening and dies under the door where the transition sits. A 3-foot doorway in a 5-inch jamb is a bit over a square foot of floor. Ten doorways is over twelve square feet, five or six planks nobody counted.
Where two rooms meet and the flooring changes, decide which side of the threshold belongs to which room and be consistent, or you'll count that strip twice. If you're planning how the materials meet, we wrote a piece on flooring transitions between rooms.
Old DMV houses aren't square
Quick answer
Measure each direction in three places, at both ends and in the middle, and use the biggest number. In a 1940s Alexandria colonial the two ends of the same room often differ by an inch or two.
This region is full of houses that have moved. Pre-war colonials in Alexandria and Arlington, Cape Cods that have been added onto, split levels from the 70s in Vienna and Annandale sitting on soil that swells and shrinks with the season. Opposite walls in those houses are rarely parallel to the inch.
An installer plans around it. Out of square shows up as a tapered cut along the last wall, and a plank floor started square to one wall ends up out of parallel with the other. That's normal work, and it costs material. If you measure the narrow end of a room and order to that number, you're short before anybody opens a box.
⚠️ Watch out
Out of square is a walls problem. Out of level is a subfloor problem, and you find it with a long straightedge or a level, not a tape. If a room is badly out of square, check level too, because both usually trace back to the same settling. Here's what floor leveling costs and when it's actually needed.
What you deduct and what you don't
Quick answer
Deduct permanent things the floor stops at: a fixed island, a hearth, a built-in cabinet run. Don't deduct the fridge or dishwasher bay, because the flooring runs under them. Stairs come out entirely and get priced separately.
The test is simple. Will the crew lay flooring on that patch of subfloor? If yes, it counts. Appliance bays count, because a dishwasher has to be able to come out one day and a fridge sits on the finished floor. A cabinet run doesn't count, because the cabinets land on the subfloor and the flooring stops at the toe kick.
An island is a judgment call and depends on whether it's fixed. A permanent island on its own base gets deducted. A rolling one is just furniture, and the floor goes under it.
Stairs are the one thing you shouldn't try to convert into square feet. They're quoted per tread and riser because the labor has nothing to do with area, and the material is a different product. We break down what hardwood stairs cost separately for exactly that reason.
Don't use the listing square footage
Quick answer
The number on your listing or tax record is gross living area. It's measured to the outside of the exterior walls and includes the walls themselves, the stairs, the closets you're not touching and rooms you're not doing. It's bigger than the floor you're replacing in almost every case.
People hand us this number all the time and it's the wrong tool. A house listed at 2,200 square feet might have 1,400 square feet of floor you want replaced. Interior and exterior walls alone eat a real slice of it, the staircase gets counted as area on both levels in most conventions, and the total a listing advertises often folds in a finished basement that was measured a different way, or a room with tile you're keeping.
It's fine for a first gut check on budget. It's not fine for ordering material, and it's not what a quote should be built on. If you're pricing a whole house, our whole-house flooring cost guide works from real floor area instead.
How much waste to add
Quick answer
Waste depends on the layout and the material, not on a single rule. Straight lay in a simple rectangular room is about 5 to 10 percent. Diagonal is around 15. Herringbone, chevron and patterned tile are 20 percent and up. Add more for lots of small rooms.
Waste is the offcuts. Every row that ends at a wall leaves a piece, and only some of those pieces are long enough to start the next row. The busier the pattern and the more corners in the space, the more of them go in the bin.
| Layout | Typical waste to add | Why |
|---|---|---|
| Straight lay, open room | 5 to 10% | Long uninterrupted rows, most offcuts start the next row |
| Straight lay, lots of small rooms | 10 to 12% | Every room restarts the pattern and ends in fresh cuts |
| Diagonal (45 degrees) | About 15% | Every plank meets the wall at an angle, both ends get cut |
| Herringbone or chevron | 20% or more | Fixed piece length, perimeter is all angled cuts |
| Large-format or patterned tile | 15 to 20% | Cuts can't be reused, and tiles break in the cutting |
| Wide or long planks | Toward the top of the range | Bigger boards, bigger leftovers, fewer usable offcuts |
Two more things push waste up. Buying a product with heavy grain or color variation means the installer is sorting boxes and setting some boards aside to keep the floor from looking blotchy. And a floor with a long feature run, like herringbone against a straight lay, is really two layouts with two waste numbers.
Keep the leftovers. A few spare planks in the crawlspace are worth more than the money back, because a damaged board five years from now needs a match and production runs change.
Carpet isn't sold in square feet
Quick answer
Carpet comes off a roll, and most rolls are 12 feet wide. Some styles come in 13 feet 6 or 15. Your room's dimensions relative to that roll width decide the order, which is why a carpet number can jump for no reason a calculator would see.
Say a bedroom is 12 by 14. That's 168 square feet, and it takes a 14-foot length of 12-foot carpet with no seam. Clean.
Now make it 13 by 14. It's 182 square feet, about 8 percent more floor. But 13 feet doesn't fit across a 12-foot roll, so you either buy 15-foot goods if that style offers them, or you buy a 14-foot length plus a strip to fill the extra foot, and you have a seam. Either way the material bill jumps well past 8 percent.
That's why a carpet quote can look strange against a plank quote for the same room, and why the shape of a room matters as much as its area. It's also why seam placement is worth asking about: a seam in a doorway or a traffic lane will show first. Our carpet installation cost breakdown and the carpet padding guide cover the rest of what goes into that number.
Turning square feet into boxes
Quick answer
Divide your total including waste by the coverage printed on the box, then round up to a whole box. Order the whole job in one go so every box comes from the same production run.
Box coverage varies by product, so read the label rather than assuming. An example with round numbers: a 12 by 15 room is 180 square feet, its 4 by 5 closet adds 20, so 200 square feet of floor. Add 10 percent for a straight lay and you need 220. If that product covers 20 square feet a box, that's 11 boxes.
Order it all at once. Flooring is made in batches, and the batch is marked on the box as a dye lot, run or lot number. Two boxes from different runs of the same product can differ slightly in color or in the gloss of the finish, which nobody notices in a store and everybody notices in a hallway.
💡 Key takeaway
If you're buying the material yourself, being short is expensive and being over is cheap. A second order costs you a delivery, a possible run mismatch, and a crew standing around waiting for it.
Why our number won't match yours
Quick answer
Expect a difference, usually a few percent. We measure the same floor you did, then add doorways, closets and the waste your layout needs. Our quote is priced on installed floor area, and the waste sits inside our price rather than on top of it.
Your number is for budgeting. It's useful for that, and doing it yourself before anyone visits means you can sanity check a quote instead of taking it on faith. Multiply your square footage by an all-in rate and you're close: LVP is $6.50 a square foot with us, hardwood $9.50, laminate $4, carpet $3.25, and each of those includes the material, the installation, and hauling the old floor away.
What we do differently on the visit is check the things a tape can't tell you. Whether the subfloor is flat enough for the product you picked, how far out of square the room runs, where the transitions land, and whether the existing floor comes up easily or fights. That's what turns a square footage into a price that doesn't move later. If you want to know what makes quotes move, we listed the charges that show up after the fact in the flooring business.
FAQs about measuring for flooring
How do I calculate square footage for flooring?
Measure each rectangle of floor in feet, multiply length by width, and add the rectangles together. Add closets and doorway pockets. Then add waste for the layout, roughly 5 to 10 percent for a straight lay and 15 to 20 percent for diagonal or herringbone.
How many square feet is a 12x12 room?
144 square feet, before waste. For a straight-lay plank floor you'd order about 152 to 158 square feet, and more if there's a closet or the layout runs diagonally. Add each closet separately as its own small rectangle.
How much extra flooring should I buy?
About 5 to 10 percent over your measured area for a straight lay in open rooms, around 15 percent for a diagonal, and 20 percent or more for herringbone or patterned tile. Add toward the top of the range when the house has many small rooms.
Do I include closets when measuring for flooring?
Yes, if the flooring goes in them. Measure each closet as its own rectangle and add it to the room total. Also add the floor inside each doorway, where the planks run through the jamb to the middle of the threshold.
Can I use my home's listed square footage for a flooring quote?
No. Listing and tax-record square footage is gross living area, measured to the outside of the exterior walls. It includes the walls, stairs and rooms you aren't touching, so it's almost always bigger than the floor you're replacing.
Why is my carpet quote higher per square foot than expected?
Carpet comes off a roll that's usually 12 feet wide. If a room is wider than the roll you either upgrade to wider goods or add a seam and a filler strip, and either one buys more carpet than the room's area suggests.
Does Potomac Floors charge for measuring?
No. We measure and quote for free anywhere in our DMV service area, and the quote is all-in: material, installation and removal of the old floor. Measuring it yourself first is still worth doing, so you can check our number against yours.
Bottom line
Length times width gets you most of the way there. Rectangles, closets, doorways, and a check that the room is actually square get you the rest. Convert inches properly, round up, and keep every room on its own line.
Then add waste to match the layout you picked, not a flat ten percent. Straight lay is cheap on offcuts. Herringbone is expensive on them. Carpet plays by roll widths instead of square feet, and stairs aren't square footage at all.
We measure for free across Northern Virginia, DC and Maryland, and we'll show you the numbers we took so you can hold them next to yours. Check what your total costs at our all-in rates on the hardwood cost per square foot page, see how we handle a quote you already have on beat any quote, or book a free estimate and we'll walk the floor with a tape.