Linear Feet vs Square Feet Calculator

This calculator converts between linear feet (length) and square feet (area) when you know the width of the material or space. Enter the linear feet and the width in feet, and it returns the square footage; or enter square feet and width to get linear feet. The result is the area covered (or length needed) based on the relationship: square feet = linear feet × width.

Formula

The core formula is straightforward:

• Square feet (sq ft) = Linear feet (ft) × Width (ft)
• Linear feet (ft) = Square feet (sq ft) ÷ Width (ft)

Where:

• Linear feet – a measure of length in the imperial/US customary system (1 ft = 12 inches = 0.3048 m).
• Width – the perpendicular dimension, also in feet. If you are working with a board, roll, or room, this is the constant width.
• Square feet – a measure of area (1 sq ft = 1 ft × 1 ft = 0.0929 m²).

This formula assumes a rectangle where the width is constant along the entire length. For irregular shapes, you would need to break the area into rectangles or use a different geometric formula.

Worked Example

Using the calculator defaults: linear feet = 100 ft, width = 1 ft.

1. Square feet = 100 ft × 1 ft = 100 sq ft
2. If you instead have 100 sq ft and a width of 1 ft, linear feet = 100 sq ft ÷ 1 ft = 100 ft.

Both results match the calculator’s output (100.00). The calculator shows the second output as a convenience: it recalculates linear feet from the square feet you entered, which is useful when you want to verify or convert back.

Why the Distinction Matters

Linear feet and square feet are often confused because both use the word “feet.� But they measure different dimensions:

• Linear feet – length only. Used for fencing, baseboards, trim, fabric, rope, or any material sold by the foot.
• Square feet – area (length × width). Used for flooring, carpet, paint coverage, land area, or tile.

For example, a 10-foot-long board that is 1 foot wide covers 10 square feet. The same board that is 2 feet wide covers 20 square feet. The linear footage is the same (10 ft), but the area doubles because the width changed.

How to Choose the Right Measurement

Your choice depends on how the material is sold or what you are trying to calculate:

• Buying lumber or trim – usually sold per linear foot. You measure the total length needed.
• Buying carpet or flooring – usually sold per square foot (or per square yard). You measure the room’s floor area.
• Painting walls – you need square footage of the wall surface to estimate paint coverage.
• Fencing – often quoted per linear foot of fence, but you might need to know the area of the panels if they are solid.

If you are comparing prices, always check the unit: $2 per linear foot is not the same as $2 per square foot unless the width is 1 foot.

Common Mistakes and Misconceptions

One frequent error is assuming that linear feet equals square feet when the width is not 1 foot. For example, a 12-foot-long board that is 6 inches (0.5 ft) wide covers 6 square feet, not 12. Another mistake is mixing units: if you measure width in inches, you must convert to feet first (divide by 12).

Also, be careful with “board feet� in lumber – that is a different unit (1 board foot = 1 ft × 1 ft × 1 inch thick). This calculator does not handle board feet; it only converts between length and area for a given width.

Rounding errors can add up. If you are calculating material for a project, always round up to the nearest whole unit (e.g., buy 10% extra) to account for waste and cuts.

Limits of the Formula

The formula assumes a perfect rectangle with a constant width. It does not work for:

• Irregular shapes (L-shaped rooms, circles, triangles) – you need area formulas for those.
• Materials with variable width (e.g., a tapering board).
• Three-dimensional volumes (cubic feet).

For a circle, area = π × radius²; for a triangle, area = ½ × base × height. This calculator is only for linear-to-square conversions when the width is uniform.

Frequently Asked Questions

How many square feet are in 100 linear feet?
It depends on the width. If the width is 1 foot, 100 linear feet = 100 square feet. If the width is 2 feet, it’s 200 square feet. Use the formula: square feet = linear feet × width.

How do I convert square feet to linear feet?
Divide the square footage by the width in feet. For example, 120 sq ft of flooring with 2-ft-wide planks gives 60 linear feet (120 ÷ 2 = 60).

What is the difference between linear feet and square feet?
Linear feet measure length (one dimension); square feet measure area (two dimensions). A 10-ft-long board is 10 linear feet regardless of width, but its square footage changes with width.

Can I use this calculator for inches?
Yes, but convert inches to feet first (divide by 12). If you enter width in inches, the result will be off by a factor of 12. Better to use consistent units.

Why do some materials list price per linear foot and others per square foot?
It depends on how the product is sold. Items with a fixed width (like carpet rolls, lumber, or trim) are often priced per linear foot because the width is standard. Items like tile or land are priced per square foot because the shape varies.

Does this work for metric units?
No, the calculator uses feet. For meters, the same relationship holds: square meters = linear meters × width in meters. Just substitute meters for feet.

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in lf | Linear feet | ft | 100 | 0
in w | Width | ft | 1 | 0
out sf | Square feet | sq ft | lf * w | 2
out lf2 | Linear feet (from sq ft) | ft | sf / w | 2