Linear Feet vs Square Feet: Which One Are You Buying?
Which materials use which
| Sold by linear foot | Sold by square foot |
|---|---|
| Baseboard, crown, casing, quarter round | Flooring, tile, carpet |
| Countertop (at a standard depth) | Paint coverage, drywall |
| Fencing, railing, gutter, drip edge | Roofing (though quoted in squares) |
| Lumber, moulding, pipe, cable | Sod, mulch coverage, patio slabs |
| Ridge cap, starter strip, valley metal | Underlayment, house wrap, insulation batts |
The conversion, and its one condition
You can convert between the two only when one dimension is fixed and known:
square feet = linear feet × width in feet
Examples where that works:
- A 25 in deep countertop run of 14 linear feet: 25 ÷ 12 = 2.08 ft, so 14 × 2.08 = 29.2 sq ft.
- A 3 ft wide walkway 40 ft long: 40 × 3 = 120 sq ft of pavers or concrete.
- A roll of underlayment 3 ft wide and 100 ft long: 300 sq ft of coverage.
Where it does not work is a bare linear figure with no width. "I need 60 linear feet of baseboard" carries no area at all, and no amount of arithmetic turns it into square feet — nor does it need to, because baseboard is priced by the foot.
The two mistakes that cost money
- Quoting a perimeter as an area. Baseboard, quarter round and crown are perimeter items. For a 12 × 10 ft room the flooring is 120 sq ft but the baseboard is 44 linear feet minus doorways — completely different numbers describing the same room.
- Assuming a supplier's "per foot" price means square foot. On trim, moulding, gutter and countertop it almost always means linear foot. On flooring and tile it almost always means square foot. Confirm which, especially on countertop, where the difference is large.
Measuring a perimeter properly
For baseboard and trim:
- Add up all wall lengths at floor level: for a rectangle that is 2 × (length + width).
- Subtract door openings — typically 3 ft each, and cased openings can be much wider.
- Add 10% for mitre cuts and mistakes. Corners are where trim gets ruined.
- Buy in the longest lengths that will fit in your vehicle and through your door: fewer joints on a long wall looks markedly better.
For a 12 × 10 ft room with two 3 ft doorways: 2 × (12 + 10) = 44, minus 6 = 38 linear feet, plus 10% = 42 linear feet to buy.
What about "board feet"?
A third unit, used for rough lumber, and a volume rather than a length or an area:
board feet = thickness (in) × width (in) × length (ft) ÷ 12
One board foot is 144 cubic inches — a piece 1 in thick, 12 in wide and 1 ft long. Hardwood suppliers price by the board foot; home centres usually price dimensional softwood by the piece or by the linear foot. Do not mix the three.
Calculate the area of a room or any regular shape, add rooms into a running total, and convert the result into square yards, square meters and a material cost.
Frequently asked questions
What is the difference between linear feet and square feet?
Linear feet measure length along one dimension, such as a run of baseboard or fencing. Square feet measure area, length times width, such as a floor. They describe different things and are not interchangeable.
How do I convert linear feet to square feet?
Multiply the linear feet by the width in feet — but only when the width is fixed and known. A 14 linear foot countertop 25 inches deep is 14 times 2.08, or about 29 square feet. Without a width, a linear figure cannot become an area.
Is baseboard sold by linear foot or square foot?
Linear foot. So are crown moulding, casing, quarter round, gutter, fencing and railing. Measure the perimeter, subtract door openings, and add about 10 percent for mitre cuts.
What is a board foot?
A unit of volume used for rough lumber: thickness in inches times width in inches times length in feet, divided by 12. One board foot equals a piece 1 inch thick, 12 inches wide and 1 foot long.
- How to Measure the Square Footage of a Room
- Square Feet, Square Yards and Square Meters: Converting Without Errors
- How Much Flooring Do I Need?
- How to Calculate the Square Footage of a House