Calculators · Hardwood Flooring Calculator

Hardwood floors

Hardwood Flooring Calculator

Add your rooms to get the cartons of hardwood to buy, spare cartons, and the rows with the expansion space.

Area 1

Shape

Length

Width

Waste, from maker guides

Pick one to fill the box next to it, or keep Custom.

Waste to add (%)

Empty counts as 0%.

Square feet per carton

Optional. Read it on the carton. Empty skips the cartons.

Spare cartons

Optional. A whole number. Needs the square feet per carton.

Boards per carton

Optional. Needs the square feet per carton too.

Room width across the rows

Optional. The side the boards run away from, like 12 or 12'6".

Board width (in)

Optional. The face width you see, like 3 1/4 or 5.

Expansion space, from maker guides

Pick one to fill the box next to it, or keep Custom.

Expansion space (in)

Per wall, like 3/4 or 0.75. Used for the rows.

How to figure the cartons of hardwood

Hardwood is sold in cartons that list the square feet they cover. The job is to turn the floor area into whole cartons, and to leave room for boards you will not use. You can read each step in the result above.

Area. Multiply length by width in feet for each room and add them. A 14 ft by 12 ft room is 168 square feet.
Waste. Mullican, Shaw and Mohawk all say 5% for a straight layout. With 5% you multiply by 1.05, so 168 becomes 176.4 square feet.
Cartons. Divide by the square feet in one carton. With 20 square feet per carton, 176.4 ÷ 20 = 8.82.
Round up. You need 9 cartons, which is 180 square feet.
Spare cartons. If you want some for later repairs, type how many and they are added at the end.

Why hardwood waste is different

With hardwood, part of the extra is not for cuts. Wood is a natural product and the grade allows some defects. The guides we opened (checked October 2026) put it this way:

Maker	What the guide says
Mullican	Add 5% so the installer can cull out boards with defects, minor imperfections or character you do not want. Its formula says 5% to 7%. Add more for lower grades and 10% to 15% for diagonal. Buy 1 or 2 extra cartons for repairs.
Shaw (2010 guide)	A 5% cutting allowance, depending on the layout. Diagonal, herringbone or bordered installs need a higher percentage.
Mohawk (engineered)	Buy an additional 5% to allow for cuts, and an additional 10% if installing diagonally.
Somerset	Industry standards allow a variance from grading and manufacturing tolerances of 5%.

Mohawk does not say whether its extra 10% for diagonal is on top of the 5% or the whole figure, so we quote it as written and do not guess. The waste list in the calculator offers 5%, and 10% and 15% from the Mullican range. Type any other number you prefer.

Example: a 14 ft by 12 ft room

Step	5%, straight	15%, diagonal
Area	14 × 12 = 168 sq ft	14 × 12 = 168 sq ft
With waste	168 × 1.05 = 176.4 sq ft	168 × 1.15 = 193.2 sq ft
Cartons of 20 sq ft	176.4 ÷ 20 = 8.82	193.2 ÷ 20 = 9.66
Rounded up	9 cartons	10 cartons
With 1 spare carton	10 cartons, 200 sq ft	11 cartons, 220 sq ft

With the 5% figure and one spare carton you leave the store with 200 square feet for a 168 square foot floor, so 32 square feet are left over.

Expansion space, rows and the last row

Wood moves with the humidity, so the floor needs a gap at the walls. Somerset and Shaw both say 3/4 inch, and Somerset credits the National Wood Flooring Association (NWFA) installation guidelines for it. We could not open the NWFA guide itself, so we cite it only through them. Mohawk gives a different rule for its engineered floors: the space equals the thickness of the product, 3/8 inch for a 3/8 inch floor and 1/2 inch for a 1/2 inch floor. The calculator takes the room width across the rows, removes the space on both walls and divides by the board width. Here is a 12 ft wide room with 3/4 inch at each wall:

Board width	Space for boards	Full rows	Last row	Rows in all
2 1/4 in	142.5 in	63	0.75 in	64
3 1/4 in	142.5 in	43	2.75 in	44
5 in	142.5 in	28	2.50 in	29

A very thin last row is a problem, and the guides say what to do. Shaw says that if the last row is 1 inch or less you glue those pieces to the last full row you have not installed yet and install them together. Mohawk asks you to try to keep at least 2 inches on a scribed plank along the wall. When your last row is that narrow, the calculator shows the matching note. Shaw also says floors wider than 20 feet may need more or less spacing between rows, depending on the climate and the time of year.

Before you install

Subfloor. Mohawk asks for flat to within 3/16 inch over 10 feet or 1/8 inch over 6 feet. Shaw asks for the same two numbers.
Humidity. Mohawk asks for the heating and cooling system on for at least 5 days at 65 to 75 degrees and 35% to 55% relative humidity. Somerset quotes 30% to 50% from the NWFA.
Acclimation. Shaw says a minimum of 72 hours, or as long as needed to reach moisture equilibrium.
Which floor. The Shaw and Somerset guides we opened are for solid hardwood. Mohawk’s is for engineered hardwood. Check which one you are buying.

Other floors and tools

To add up a whole house with different floors, use the flooring calculator. For floating floors there is the laminate flooring calculator and the vinyl plank flooring calculator. If you are buying lumber by volume instead of by the carton, try the board foot calculator.

What this tool does not cover

Layout. It counts from the area. It does not plan where the cuts fall or the stagger of the end joints.
Grade and species. The waste comes from maker guides and a lower grade can need more. The choice is yours.
Price. No prices are shown, because they change by store and region. Take your numbers to your supplier and ask for a quote.

Frequently asked questions

How much hardwood flooring do I need for my room?

Multiply the length by the width in feet to get the area, then add the waste your maker asks for. Mullican, Shaw and Mohawk say 5% for a straight layout. Divide by the square feet in a carton and round up. A 14 ft by 12 ft room is 168 square feet. With 5% that is 176.4 square feet, and with 20 square feet in a carton that is 8.82, so 9 cartons.

Why add 5% to hardwood flooring if the room is simple?

Mullican says the 5% lets the installer cull out boards with manufacturing defects, minor imperfections or character you do not want. Somerset quotes the industry standard as a grading and manufacturing variance of 5%. Mohawk says 5% for cuts. So some of the 5% is for boards you will not use, and cuts at the walls come on top of that.

How many planks of wood do I need?

Fill in the square feet per carton and the boards per carton. The calculator divides the square feet per carton by the boards per carton to get the area of one board, then divides your total with waste by that. With 20 square feet and 10 boards in a carton, the 176.4 square feet above needs 89 boards, and the 9 cartons hold 90. Boards in a carton often come in mixed lengths, so treat the count as a guide.

How much expansion space should I leave around hardwood flooring?

Somerset and Shaw both say to leave 3/4 inch between the wood and the walls or other obstructions, and Somerset credits the National Wood Flooring Association guidelines for it. Mohawk says that for its engineered floors the space equals the thickness of the product, so 3/8 inch for a 3/8 inch floor and 1/2 inch for a 1/2 inch floor. Follow the guide of your own floor.

How much extra should I buy for a diagonal or herringbone layout?

Mullican says to add 10% to 15% for a diagonal layout, since the boards are cut at an angle. Shaw says diagonal, herringbone or bordered layouts need a higher percentage than its 5% and does not give one. Mohawk says an additional 10% if installing diagonally. The calculator offers 10% and 15% from the Mullican range and lets you type your own.

Should I buy spare cartons of hardwood?

Mullican recommends buying 1 or 2 additional cartons. It says they can be used later for repairs if boards are damaged by water leaks or other job-site problems. Type the number of spare cartons in the calculator and it adds them to the count and to the square feet you will have left.

How long should hardwood acclimate before installation?

Shaw says to acclimate solid hardwood for a minimum of 72 hours, or as long as needed to reach moisture equilibrium with the job site. It also asks for the heating and cooling system to run for at least 7 days beforehand, at 65 to 75 degrees and 35% to 55% relative humidity. Your own maker may ask for something else.