Methodology
Last updated: July 19, 2026
How HomeMaterialBase turns dimensions into yards, bags, gallons, and pitch. Arithmetic runs in your browser. These are planning estimates for a store run — not engineering advice and not a contractor bid.
Start shopping: concrete calculator. Site story: about.
Summary
| Topic | How we estimate |
|---|---|
| Concrete volume | Slab / pad: L × W × (thickness ÷ 12) → cu ft. Cylindrical holes: n × π r² h. Order volume = volume × (1 + waste%). Yards = cu ft ÷ 27. |
| Concrete bags | Bags = ceil(order cu ft ÷ bag yield). Defaults: 40 lb ≈ 0.30 cu ft, 60 lb ≈ 0.45, 80 lb ≈ 0.60. Override when the bag label differs. |
| Gravel / mulch / topsoil | Area × (depth ÷ 12) → cu ft → yards with waste. Optional tons = yards × density (tons/yd³). Mulch bags = ceil(order cu ft ÷ bag cu ft), default 2 cu ft bags. |
| Paint | Wall sq ft = 2 × (L + W) × H, minus doors/windows (defaults 20 / 15 sq ft). Gallons = ceil(paintable × coats × (1 + waste%) ÷ coverage). Default coverage 350 sq ft/gal. |
| Roof pitch | pitch_on_12 = (rise / run) × 12; degrees = arctan(rise/run); slope_factor = √(1 + (rise/run)²). Optional surface ≈ footprint × slope factor. |
| Waste | Default 10% on most volume and paint tools — a slider, not a hidden fee. Spillage, over-dig, and uneven beds eat material; you set the percent. |
Volumes and waste
Cover materials (gravel, mulch, topsoil) and concrete share the same volume idea: fill a shape, convert to cubic feet, then to cubic yards (27 cu ft per yard). Waste multiplies the order amount so you are not one wheelbarrow short. Ten percent is a common starting guess for DIY pads and beds; rocky digs and odd shapes may want more.
Bag yields
Concrete bag defaults follow common US bag yield rules of thumb. Brands and mix types differ — high-early, gravel-mix, and mortar bags can land elsewhere. If the bag print says 0.45 cu ft for a 60 lb sack, type that in. We ceil bag counts so the ticket never rounds down into a half-bag fantasy.
Mulch bag math uses a bag volume (default 2 cu ft). Nursery SKUs vary; change the field when the pallet tag disagrees.
Paint coverage
Default 350 sq ft per gallon per coat is a conservative smooth-wall number. Texture, dark-to-light color changes, and thrifty paint eat coverage. The can label wins. Primer is a separate line with its own coverage when you enable it.
Roof pitch
Pitch is rise over run, usually spoken as X-in-12. Degrees and slope factor fall out of that ratio. Multiplying a flat footprint by the slope factor estimates roof surface area for materials — it does not size rafters, price a tear-off, or walk your ridge.
What we do not model
- Structural design, mix design, PSI, or rebar schedules
- Labor hours, equipment, delivery fees, or markup
- Compaction specs, contamination testing, or bonded bids
- Multi-plane roofs with hips, valleys, and dormers as one blob
Wrong default or a formula that does not match a bag label? Email contact@homematerialbase.com.
Estimate only — not a contractor bid. Confirm bag yields, coverage rates, and truck quotes with your supplier before you order.