Builders’ merchants price trim, lumber, fencing and countertops by the linear foot, while floors, decks and walls are measured in square feet. Converting between them trips a lot of people up, because a linear foot measures length only. To turn it into an area, you always need one more number: the width.
What is a linear foot?
A linear foot is one foot of length measured in a straight line, regardless of how wide or thick the item is. A 10-foot board is 10 linear feet long whether it is 2 inches or 12 inches wide. Square feet, by contrast, measure the area something covers: length × width.
The formulas
Square feet = linear feet × width (ft)
Linear feet = square feet ÷ width (ft)
If the width is in inches, divide it by 12 first. A 6-inch width is 0.5 ft; a 5.5-inch width is 0.4583 ft; a 3.5-inch width is 0.2917 ft.
Beware of online claims such as “10 linear feet equals 100 square feet”. That is only true if the material happens to be 10 feet wide.
Worked examples
- Carpet roll: 20 linear feet cut from a 12 ft wide roll covers 20 × 12 = 240 sq ft.
- Countertop: 12 linear feet of a standard 25.5-inch-deep counter is 12 × (25.5 ÷ 12) = 25.5 sq ft of surface.
- Deck boards: to cover a 200 sq ft deck with 5.5-inch-wide boards, you need 200 ÷ (5.5 ÷ 12) = 436.4 linear feet, or about 480 linear feet with 10% extra for cuts.
- Garden bed edging vs soil: a 15 × 4 ft bed needs 2 × (15 + 4) = 38 linear feet of edging around it, and covers 15 × 4 = 60 sq ft inside.
Linear feet needed per 100 square feet
For boards and planks, the actual width (not the nominal size) is what matters. A “1×6” deck board is actually about 5.5 inches wide.
| Material width | Width in feet | Linear feet per 100 sq ft | With 10% extra |
|---|---|---|---|
| 3.5 in (e.g. 1×4) | 0.2917 ft | 342.9 | 377.1 |
| 5.5 in (e.g. 1×6, 5/4×6) | 0.4583 ft | 218.2 | 240 |
| 7.25 in (e.g. 1×8) | 0.6042 ft | 165.5 | 182.1 |
| 9.25 in (e.g. 1×10) | 0.7708 ft | 129.7 | 142.7 |
| 12 in | 1 ft | 100 | 110 |
| 4 ft (sheet goods) | 4 ft | 25 | 27.5 |
Real decks also have small gaps between boards, which very slightly reduces the number of boards needed. The figures above are a safe estimate.
Things measured only in linear feet
Some items never need converting because they run along an edge: baseboard, crown molding, door casing, fencing, gutters and edging. For these, measure the perimeter or run length. A 12 × 14 ft room has a perimeter of 2 × (12 + 14) = 52 linear feet, minus doorways, for baseboard.
Linear feet vs board feet
Hardwood lumber is often priced by the board foot, which is a volume: 12 inches × 12 inches × 1 inch thick. A board 1 inch thick, 6 inches wide and 8 feet long contains 1 × 6 × 96 ÷ 144 = 4 board feet. Don’t mix board feet with linear or square feet when comparing prices.
Common mistakes
- Using the nominal size. A “2×6” board is really about 1.5 × 5.5 inches. Always use the actual width printed on the label or in the product details.
- Forgetting unit conversion. Multiplying linear feet by a width in inches gives a number twelve times too big.
- Ignoring waste. Cuts, end joints and damaged pieces use up material, so order 5–10% more than the exact figure.
- Converting things that don’t need it. Baseboard and fencing are bought by length; you only need the run length, not an area.
Quick checklist
- Find the true width of the material, and convert inches to feet.
- Multiply linear feet by width to get square feet, or divide square feet by width to get linear feet.
- Add 5–10% for cuts and waste.
- Use the flooring calculator or square footage calculator to get the area first.
Frequently asked questions
How do I convert linear feet to square feet?
Multiply the linear feet by the width of the material in feet. 50 linear feet of 6-inch boards (0.5 ft) covers 25 square feet.
How many square feet is 10 linear feet?
It depends on the width. Ten linear feet of a 1-foot-wide material is 10 square feet; of a 12-foot-wide carpet roll it is 120 square feet. Without a width there is no single answer.
How do I convert square feet to linear feet?
Divide the square feet by the width in feet. To cover 100 square feet with 5.5-inch boards, divide 100 by 0.4583 to get about 218 linear feet.
Is a linear foot the same as a foot?
Yes. A linear foot is simply one foot of length, measured in a straight line. The word “linear” is used to make clear it is not an area.
What is the difference between linear feet and board feet?
Linear feet measure length only. Board feet measure the volume of lumber: one board foot is 12 × 12 × 1 inch, or 144 cubic inches.
What is sold by the linear foot?
Trim, baseboard, crown molding, fencing, gutters, lumber, countertops and fabric are commonly priced per linear foot.