Methodology & sources
Every Calculator Hub estimate uses the formulas and named constants below. We show the same breakdown in the tool and in PDF downloads.
Every Calculator Hub estimate uses the formulas and named constants below. We show the same breakdown in each tool and in PDF downloads so you can verify our math against your supplier's specs. Constants cite manufacturer labels or industry rules of thumb — when your bag or paint can differs, override the defaults in the calculator.
Concrete
Concrete volume starts as a simple geometric calculation in cubic feet, then converts to cubic yards for ready-mix orders or bag counts for retail mix. We apply a default 10% waste factor on all pours because spillage and subgrade variation are routine on job sites — not because we want you to over-buy, but because running out mid-pour is costly.
Formulas
- Volume (ft³) = length (ft) × width (ft) × thickness (in) ÷ 12
- Cubic yards = ft³ ÷ 27
- Bags = ceil(ft³ ÷ bag_yield_ft³ × (1 + waste))
- Column: ft³ = π × (diameter_in ÷ 24)² × height (ft)
Constants
- 80 lb bag yield: 0.60 ft³Source: Quikrete 5000 / Sakrete High-Strength — verify current bag label
- 60 lb bag yield: 0.45 ft³Source: Manufacturer spec sheets
- 40 lb bag yield: 0.30 ft³Source: Manufacturer spec sheets
- Default waste: 10%Source: Industry rule of thumb for spillage and over-excavation
- Ready-mix is typically ordered in 0.25 yd³ increments — we round order yards accordingly.
- PSI and mix design are out of scope — consult your supplier for structural specs.
- Round columns use diameter in inches divided by 24 to get radius in feet before applying πr²h.
- When volume exceeds ~1.5 yd³, compare bag cost and labor against a short-load ready-mix quote.
Mulch
Mulch quantity is pure volume: bed area times depth. The same math applies to wood chips, bark, rubber, and stone — only bulk density and delivery method change. We default to 2 ft³ retail bags because that is the most common US bag size at big-box and nursery chains.
Formulas
- Volume (ft³) = area (ft²) × depth (in) ÷ 12
- Bags = ceil(ft³ ÷ 2) for standard 2 ft³ bags
- Bulk yards = ft³ ÷ 27
Constants
- Retail bag size: 2 ft³Source: Common US bagged mulch (2 cu ft)
- Coverage check: ~100 ft² per yd³ at 3 inSource: Landscaping rule of thumb — sanity-check calculator output
- Gravel delivery weight: ~1.4 US tons per yd³Source: Crushed stone/gravel industry rule of thumb — verify with your quarry or supplier
- Wood and rubber mulch use volume-only math; stone/gravel adds delivery weight at ~1.4 US tons per yd³ (crushed stone industry rule of thumb — verify with your quarry).
- Recommended depth for new beds is 3 inches after settling; top-dress 1–2 inches annually.
- Pull mulch away from tree trunks — deep mulch volcanoes cause bark decay.
Tile
Tile counts begin with project area divided by nominal tile area. Grout joint width is ignored in our MVP — using nominal tile size is slightly conservative versus net coverage. Waste factors reflect cut geometry: straight layouts waste less than diagonal or herringbone patterns.
Formulas
- Tile area (ft²) = (width_in × height_in) ÷ 144
- Tiles = ceil(project_ft² ÷ tile_ft² × (1 + waste))
- Boxes = ceil(tiles ÷ tiles_per_box)
Constants
- Straight-lay waste: 10%Source: Standard installer allowance
- Diagonal waste: 15%Source: Higher cut waste on diagonal/herringbone
- Grout joint width is ignored in MVP counts — slightly conservative vs. nominal tile size.
- Always purchase full boxes; dye lots vary between production runs.
- Backsplash jobs with many outlets may need extra waste beyond 10% — consider an spare box.
Paint
Paint gallons depend on paintable wall area, manufacturer coverage on the can, and number of coats. We default to 350 ft² per gallon and two coats — typical for mid-grade interior latex on primed drywall. Deep colors, unprimed surfaces, and heavy texture reduce real-world coverage.
Formulas
- Wall area = perimeter (ft) × height (ft) − openings
- Gallons = ceil(paintable_ft² × coats ÷ coverage_ft²_per_gal)
Constants
- Default door deduction: 21 ft²Source: Typical interior door — editable in calculator
- Default window deduction: 15 ft²Source: Typical small window — editable in calculator
- Default coverage: 350 ft²/galSource: Mid-range interior latex — check your paint can
- Default coats: 2Source: Standard wall finish
- Textured walls and deep colors may reduce effective coverage — buy an extra quart on borderline jobs.
- Ceilings use length × width when calculated separately from walls.
- Primer uses the same area formula with coverage from the primer label — often one coat.
Calculator Hub provides estimates for planning purchases. Always verify quantities with your supplier, installer, or engineer for structural work. Not professional engineering or contracting advice.