How the flooring calculator works
There are two tabs, and most people use both:
- Boxes needed: enter the room size, the layout and the coverage of one box. It adds waste and tells you how many boxes to buy, how much is left over and how much underlayment you need. Add a price per square foot if you want a cost.
- Plank row layout: enter the width of the room and of one board. It shows how many rows fit, and warns you if the last row would be a thin sliver.
How much flooring do I need?
Multiply the length by the width to get the area, add any closets or halls, and subtract anything the floor will not go under, such as a kitchen island. Then add extra for waste. Boards are cut at the walls and doorways, and some are damaged or have defects.
| Layout | Extra to buy |
|---|---|
| Straight, parallel to a wall | 5 to 10% (the calculator uses 7%) |
| Diagonal | about 15% |
| Herringbone or chevron | 15 to 20% |
| Room with many corners, doors or closets | add another 3% or more |
Flooring is sold in whole boxes, so the calculator rounds up. It also shows how much you have left over. Keep the spare boards, because the same batch or colour may be discontinued when you need a repair.
The expansion gap
Flooring expands and shrinks with heat and humidity. Leave a gap along every wall and around pipes and fixed objects, which the baseboards or quarter-round then hide.
| Flooring | Typical gap |
|---|---|
| Laminate or vinyl plank | 3/8 in (about 1 cm) |
| Engineered hardwood | 1/2 in (about 1.2 cm) |
| Solid hardwood | 3/4 in (about 2 cm) |
These are common figures. Follow the instructions of the product you buy, because the maker’s rules decide whether the warranty stands.
Plan the rows before you start
Rows run across the width of the room. If the last row is only a sliver, it is hard to cut and fit, and it looks odd along the wall. Check it first:
- Take the room width and subtract the gap on both sides.
- Divide by the width of a board. The whole number is the full rows.
- Look at what is left for the last row. If it is under about 2 in, or less than a third of a board, cut the first and the last row to the same width instead. This is half of the leftover plus one board.
Which way should the boards run?
- Along the longest wall, or towards the main window, which makes the room look longer and hides the joints.
- Across the floor joists for solid hardwood nailed down.
- Along the length of a narrow hall.
Stagger the joints
End joints in neighbouring rows should be at least 6 in (15 cm) apart. Starting each row with an offcut from the last one helps cut waste, as long as the offcut is long enough.
Worked examples
A 15 × 12 ft room, straight laminate
The floor is 180 sq ft. With 7% waste you need 192.6 sq ft. At 20 sq ft per box that is 10 boxes, or 200 sq ft, with about 20 sq ft spare. The underlayment is about 189 sq ft, which is 2 rolls of 100 sq ft.
A 12 ft wide room with 7 in boards
With a 3/8 in gap each side the boards cover 143.25 in. That is 20 full rows and a last row 3.25 in wide, which is fine to use.
The same room with 7.5 in boards
You get 19 full rows and a last row of only 0.75 in. Cut the first and the last row to about 4 1/8 in instead.
Common mistakes
- Not adding waste. Running short with a different batch of flooring is a common regret.
- Forgetting the gap. Flooring that is pushed tight to the wall can buckle in summer.
- Laying over an uneven floor. Most floating floors need a subfloor flat to about 3/16 in over 10 ft.
- Not mixing boxes. Take boards from several boxes as you lay them so the shading blends.
- Skipping acclimation. Wood and some other floors should sit in the room for a few days before you lay them. Check the instructions.
Tips
- Measure each room separately, and add them up.
- Undercut door frames with an oscillating saw, so the boards slide under, and you do not have a gap to fill.
- Lay out a few rows without gluing or clicking to check the look before you commit.
- Buy the transition strips, stair nosing and quarter-round at the same time.
