Introduction
Three different “feet” run construction estimating, and mixing them up is one of the most expensive mistakes a DIYer can make. Linear feet measure a single length; square feet measure an area; board feet measure lumber volume. Each answers a different buying question.
The Linear Feet Calculator handles the core calculation: enter your total run length and a waste allowance, and it returns the required linear footage in feet and meters, plus how many stock-length pieces to buy. This guide explains the formulas behind that number — what linear feet are, how they differ from square and board feet, and how to measure runs, account for laps and joints, and size waste properly.
Linear Feet: The One-Dimensional Measure
A linear foot is a straight-line foot — the unit you get from walking a tape measure along the path the material will follow. Baseboard, casing, crown molding, deck boards, fence rails, and pipe are all bought by linear feet because their width and thickness are fixed by the profile.
Formula: perimeter runs
Linear feet = 2 × (Length + Width) − openings. For the canonical 12×14 ft room: 2 × (12 + 14) = 52 lin ft (no openings to subtract; when doorways are present, subtract each width first).
Formula: fence and deck runs
Linear feet = sum of all straight segments − gate openings. A yard with fence lines of 60, 45, 60, and 45 ft (one 4-ft gate) is 210 − 4 = 206 lin ft of picket/rail run — posts are counted separately.
Formula: waste and rounding
Order length = run length × (1 + Waste%), rounded up; pieces = order length ÷ stock length, rounded up. For the 12×14 room: 52 × 1.10 = 57.2 → 58 lin ft; 58 ÷ 8 = 7.25 → 8 pieces of 8-ft stock.
Square Feet: The Two-Dimensional Measure
Square footage multiplies length by width — the unit for anything that covers an area: flooring, paint, drywall, roofing. The 12×14 ft room has 12 × 14 = 168 sq ft of floor.
Converting between linear and square feet
Square feet = Linear feet × width in feet — a 12-ft board 6 in (0.5 ft) wide covers 6 sq ft. Conversely, linear feet = square feet ÷ width in feet: 168 sq ft of 6-in-wide decking = 336 linear feet of board (before gaps). In metric: 1 sq ft = 0.0929 m².
The classic blunder is ordering baseboard by the room’s square footage: 168 sq ft vs 52 lin ft of run is a 3.2× overbuy. The common mistakes guide catalogs this and its cousins.
Board Feet: The Lumber Volume Measure
Rough lumber and hardwoods are often priced by the board foot — 144 cubic inches of wood (a board 12 in × 12 in × 1 in). Board feet = Length (ft) × Width (in) × Thickness (in) ÷ 12. A 12-ft 1×6 = 6 board feet; a 12-ft 2×6 = 12 board feet (nominal 2-in thickness is used, not the actual 1.5 in).
When each unit applies
| Unit | Measures | Used for | Example |
|---|---|---|---|
| Linear feet | Length | Molding, trim, decking boards, fence rails, pipe | 52 lin ft of baseboard run |
| Square feet | Area | Flooring, paint, drywall, roofing | 168 sq ft of floor |
| Board feet | Volume (144 in³) | Rough lumber, hardwoods, timbers | 6 board feet in a 12-ft 1×6 |
All three can describe the same board — a 12-ft 1×6 is 12 linear feet, covers 6 square feet, and contains 6 board feet — but the price list picks one: molding per linear foot, hardwood per board foot, flooring per square foot. See the cost guide for pricing context.
Measuring Runs: The Field Technique
The formula is only as good as the tape work:
- Walk every segment. Measure each wall, fence line, or deck edge individually and write each number down — adding remembered guesses is how 2-ft errors happen.
- Measure where the material goes. Baseboard at floor level; fence lines along the ground the fence will follow — slope adds real length.
- Subtract every opening, then add segments, then waste. Doorways, gates, and fireplaces come out of the run total; waste is a multiplier on the net total, applied once, after all deductions.
The estimating guide turns this into a full step-by-step workflow for trim, decking, and fencing.
Laps, Joints, and Scarf Cuts
Long runs exceed stock lengths, so joints are part of the plan — and each joint costs a little material and must land on solid support.
Scarf joints for trim
When a wall run exceeds your stock (a 20-ft wall in 16-ft molding), join two pieces with a scarf joint — opposing 45° bevels that overlap. The overlap consumes roughly the profile’s width plus a few inches, covered by the waste allowance. Place scarf joints over studs, staggered from adjacent rows, never at inside corners.
Butt joints for decking and fencing
Deck boards and fence rails typically butt-join over a joist or post. Board ends must land on solid support — which is why post spacing and stock length interact: a 16-ft rail on 8-ft post spacing joints cleanly at every other post, while 10-ft stock wastes 2 ft per span. Choosing stock lengths that divide evenly into your spans is the biggest waste reducer; standard lengths are in the material guide.
Lap allowances
Overlapping materials — shiplap, lap siding — have an exposure smaller than the board width. Coverage math: linear feet of board = square feet of wall ÷ (exposure in feet). For 100 sq ft of wall at 5.5-in exposure (0.458 ft): 100 ÷ 0.458 = 218.3 → 219 lin ft of board, before waste.
Waste Allowances: What the Percentage Covers
Waste isn’t padding — it’s the sum of predictable losses:
- Stock-length offcuts. A 12-ft wall from 16-ft stock leaves a 4-ft cutoff; from 8-ft stock it needs 8 + 4 with zero waste.
- Corner cuts. Mitered and coped corners each consume a few inches beyond the measured run, plus test cuts.
- Defects and damage. Warped ends, mill chatter, shipping dings — the last 6 in of many boards is unusable.
- Pattern repeat. Moldings with repeating patterns must align at joints, forcing cuts at pattern boundaries.
| Situation | Suggested waste allowance |
|---|---|
| Simple straight runs, experienced installer | 5% |
| Standard interior trim, rectangular rooms | 10% |
| Fencing, long deck runs, many joints | 12–15% |
| Patterned profiles, stairs, irregular layouts | 15–20% |
For the 12×14 room at 10%: 52 × 1.10 = 57.2 → 58 lin ft (17.68 m). At 15%: 52 × 1.15 = 59.8 → 60 lin ft (18.29 m). The pro tips guide shows how to push real waste below these defaults.
Related Guides
- Complete Guide — the full linear-feet workflow with the canonical 12×14 ft worked example.
- Estimating Guide — step-by-step field measurement for trim, decking, and fence runs.
- Material Guide — stock lengths and profiles that determine joint placement and waste.
- Common Mistakes — unit mix-ups and measuring errors, with fixes.
- Pro Tips — techniques that reduce real waste below the default allowances.
- FAQ — quick answers on units, conversions, and waste.
Frequently Asked Questions
What’s the difference between linear feet and square feet?
Linear feet measure length (one dimension); square feet measure area (length × width). A 12×14 ft room has a 52-lin-ft perimeter but 168 sq ft of floor. Baseboard is bought by linear feet; flooring by square feet.
How do you calculate board feet?
Board feet = Length (ft) × Width (in) × Thickness (in) ÷ 12. A 12-ft 1×6 is 6 board feet; a 12-ft 2×6 is 12 board feet (using nominal 2-in thickness).
How many linear feet are in a 12×14 ft room’s baseboard?
Perimeter 52 lin ft; plus 10% waste = 57.2 → 58 lin ft to buy (17.68 m).
How do I convert linear feet to meters?
Multiply by 0.3048 — 1 lin ft = 0.3048 m exactly. So 58 lin ft = 17.68 m.
What is a scarf joint and how much material does it use?
A scarf joint joins two trim pieces end-to-end with overlapping 45° bevels for long runs. It consumes roughly the profile width plus a few inches per joint — covered by the standard 10% waste allowance.
Get Your Number
The three units answer three buying questions: linear feet for anything sold by length, square feet for anything covering an area, board feet for lumber priced by volume. Get the run measured, the openings subtracted, and the waste applied — then let the Linear Feet Calculator convert it to footage, meters, and stock-length piece counts. Verify the result against the formulas above before you order.
Disclaimer: Calculator results are planning estimates based on the measurements you enter. Actual material needs vary with cut waste, pattern, and site conditions. Verify quantities with your supplier and consult a licensed professional or your local building authority for structural or code-related decisions.
