How to Estimate Paint, Flooring, Concrete and Mulch Like a Contractor

Start with square footage

Almost every estimate begins with area. Measure in feet, multiply length by width for rectangles, and split L-shaped rooms into two rectangles. There are 9 square feet in a square yard and 43,560 in an acre.

Paint

Wall area is the room's perimeter times wall height, minus about 21 sq ft per door and 15 sq ft per window. One gallon covers roughly 350-400 sq ft per coat, and most walls need two coats. A 14 × 12 ft bedroom with 8 ft walls, one door and two windows needs a little over two gallons for two coats.

Flooring

Buy the room's area plus a waste allowance: 5-10% for straight layouts, 15% or more for diagonal or herringbone patterns. Divide by the coverage printed on the box and round up. Keep one spare box for future repairs - dye lots change.

Concrete

Concrete is ordered in cubic yards: length × width × thickness (in feet) ÷ 27. A 10 × 10 ft patio, 4 inches thick, needs about 1.24 cubic yards before waste. An 80 lb bag makes about 0.6 cubic feet, so larger jobs are usually cheaper with ready-mix delivery.

Mulch, gravel and topsoil

Use the same cubic-yard formula with depth in inches ÷ 12. Mulch beds usually need 2-4 inches; gravel paths 3-4 inches; driveways 4-6 inches over a compacted base. Above about two to three yards, bulk delivery normally beats bags.

Roofing

Roof area is larger than the footprint because of the slope. Multiply the footprint (including overhangs) by the pitch factor - about 1.118 for a common 6/12 roof - then add 10-15% waste. Roofers price in “squares” of 100 sq ft, and standard shingles come three bundles to a square.

Fences

Posts equal the length divided by post spacing, plus one, plus gate posts. Pickets equal the length in inches divided by picket width plus gap. Always call 811 before digging so underground utilities are marked.

Cooling a room

For window and mini-split units, a common starting point is about 20 BTU per square foot, adjusted for sun, people and kitchens. An oversized unit cools fast but leaves the air damp; an undersized one runs all day.

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