Methodology — How Every RugCalc Formula Works

RugCalc is built on one principle: show the math. Every calculator below is a transparent formula with a worked example on its own page, so you can see exactly how a result is reached — and every result is an estimate for planning, not a guarantee.

1. Our estimation principles

• US units only. All tools use feet, inches, square feet, cubic yards, tons, gallons and BTU — the units US DIYers and suppliers actually use.
• Always round up on materials. Paint to whole gallons, tile and flooring with waste, concrete to whole bags.
• Waste factors are included. Cutting, trimming, pattern matching and breakage all need spare material.
• Estimates only. Confirm final quantities with your supplier before ordering; local codes and product specs vary.

2. Area & layout

Square footage — Area (sq ft) = length × width. For walls: perimeter × wall height.

Rug size — three well-established interior-design placement rules: bedrooms leave 18–24 in of rug beyond the bed sides and foot; living rooms use the front-legs rule (front legs of furniture sit on the rug, rug 6–8 in from the wall); dining leaves ~24 in of rug beyond the table edge so chairs stay on the rug when pulled out.

Tools: Square Footage Calculator · Rug Size Calculator

3. Coverage & finishes

Paint — Wall sq ft = 2 × (length + width) × wall height, minus doors (~21 sq ft) and windows (~15 sq ft). Coverage ≈ 350–400 sq ft per gallon per coat, the standard range quoted by major paint brands (e.g. Sherwin-Williams and Behr). Total gallons = (wall sq ft ÷ coverage) × coats, rounded up.

Wallpaper — rolls = wall area ÷ usable coverage per roll, adjusted for pattern repeat.

Drywall — a 4×8 sheet covers 32 sq ft. Sheets = wall area ÷ 32, rounded up, plus ~10% for cutting.

Tile — tiles = area ÷ single-tile area, plus 10% waste for straight layouts and 15%+ for diagonal or herringbone patterns.

Flooring & carpet — flooring = area ÷ coverage per box, plus 10% waste; carpet = area ÷ 9 (to square yards), plus 10–15% for seams and pattern.

Tools: Paint · Wallpaper · Drywall · Tile · Flooring · Carpet

4. Volume & weight

Concrete — Volume (cubic yards) = (length × width × depth in ft) ÷ 27. Bag yields follow standard manufacturer specs (Quikrete-type mixes): a 50 lb bag ≈ 0.375 cu ft, 60 lb ≈ 0.45 cu ft, 80 lb ≈ 0.60 cu ft. Bags = (cubic yards × 27) ÷ yield, rounded up.

Gravel — tons = (area × depth in ft ÷ 27) × density, with crushed stone typically ~1.4–1.6 tons per cubic yard.

Mulch — volume = area × depth in ft; 1 cubic yard = 27 cu ft, and a typical bag holds 2 cu ft.

Pool volume — gallons = length × width × average depth × 7.48 (cubic feet to gallons).

Tools: Concrete · Gravel · Mulch · Pool Volume

5. Outdoor & structure

Fence — posts spaced ~8 ft on center; pickets = run length ÷ (picket width + gap).

Deck & lumber — deck area plus ~10% waste; board feet = (thickness in × width in × length ft) ÷ 12.

Paver — pavers = area ÷ paver area, plus 5–10% waste.

Sod — area ÷ pallet coverage (a pallet typically covers ~450 sq ft depending on grass type).

Stairs — risers = total rise ÷ ~7–8 in (code-compliant); treads = risers − 1.

Roof — squares = area ÷ 100; bundles = squares × 3 for standard 3-tab shingles (4 for architectural).

Tools: Fence · Deck · Lumber · Paver · Sod · Stairs · Roof

6. Environment & appliances

BTU — room BTU ≈ square feet × 20–25, adjusted for climate zone, ceiling height, sun exposure and insulation. This is the common sizing rule used by the U.S. Department of Energy and ENERGY STAR guidance for room air conditioners.

TV size — comfortable viewing distance ≈ screen diagonal × 1.6–2.5, based on THX-style recommended viewing distances.

Curtain length — rod to floor (or sill) plus hem allowance; width = window width × 1.5–2.5 for fullness.

Tools: BTU · TV Size · Curtain Length

7. Where the reference numbers come from

• Paint coverage — the 350–400 sq ft/gal range follows published specs from major paint manufacturers (Sherwin-Williams, Behr).
• Concrete bag yields — standard manufacturer yields for 50/60/80 lb bag mixes (Quikrete-type).
• BTU sizing — U.S. Department of Energy / ENERGY STAR room air-conditioner sizing guidance by climate zone.
• Rug placement — common interior-design placement conventions (18–24 in rule, front-legs rule, dining 24 in rule).
• TV viewing distance — THX-style recommended viewing distances.
• Stair code — standard IRC riser-height guidance.

Where a standard exists, we review our formula and reference values against it before release. We cite these as industry-standard rules of thumb, not as substitutes for your local building code or a supplier's product spec.

8. Disclaimer

All results are estimates for planning only. Actual needs vary with product brand, waste, layout, moisture, and local conditions. Always verify final quantities and dimensions with your supplier or a licensed professional before ordering materials. See our full disclaimer.