Principles
- One typed engine owns every formula; the interface never recomputes a value.
- Assumptions live in one file shared by all calculators, guides and Project Mode.
- Invalid input produces a named error, not a plausible-looking number.
- Costs use only prices the user entered. Current market prices are never generated.
- Where the supplied geometry is insufficient, a result is withheld instead of guessed.
Bulk materials
Area × depth converts to cubic feet, then cubic yards. Compaction is applied first where the material settles, then waste, then the purchase quantity is rounded to the order granularity. Tons use the configured density for the material; bag counts round up because bags are indivisible.
The engine recommends bags below the bag/bulk threshold and bulk above it, and shows both when the two are compared — but never converts a bag count into a fabricated bulk price.
Pavers
Paver count uses a joint-aware module dimension, so joint width is part of the arithmetic rather than a footnote. Base and bedding sand are calculated independently, each with its own depth and compaction factor. Edge restraint is derived only when the perimeter geometry is available; otherwise the result is omitted, not estimated.
Fence
Post counts are spacing-based planning estimates with corners, ends and gates counted separately from the run. Rails follow fence height; pickets or panels follow the infill type chosen, but the posts and concrete do not change with it. Concrete uses cylindrical post-hole volume from the configured hole diameter and depth. Hardware allowances are generic — not a manufacturer-specific system.
Deck
Deck quantities estimate material only: boards from area and board width with the specified gap, joists from spacing, beams and posts from the plan you supply. The engine does not determine safe spans, footing sizes, load ratings, structural adequacy or code compliance.
Concrete
Volume comes from geometry; weight uses the configured 150 lb per cubic foot normal-weight figure. Ready-mix is rounded up in delivery increments, bag counts round up by bag yield, and the bag-vs-bulk advice flips at the configured thresholds. Thin slabs trigger a thickness warning because they are commonly under-specified.
Central defaults
Every value below comes from the single assumptions file the engine reads. Where a calculator exposes an override, the override is shown next to the result it affected.
| Material | Density (tons per yd³) | Bag sizes (ft³) |
|---|---|---|
| gravel | 1.4 typical (1.2–1.7 range) | 0.5 |
| pea-gravel | 1.4 typical (1.3–1.5 range) | 0.5 |
| sand | 1.35 typical (1.25–1.6 range) | 0.5 |
| topsoil | 1.1 typical (0.9–1.4 range) | 0.75, 1, 1.5 |
| soil | 1.2 typical (1–1.5 range) | 0.75, 1, 1.5 |
| mulch | 0.35 typical (0.25–0.6 range) | 2, 3 |
| landscape-rock | 1.35 typical (1.2–1.6 range) | 0.5 |
| paver-base | 1.4 typical (1.3–1.6 range) | 0.5 |
Densities are planning defaults for the named material; supplier products vary. Enter your supplier's figures where the calculator allows it.
Sources
These are the external references cited across the guide library — published extension guidance and material reference material used to sanity-check the defaults above. Each guide cites the specific source where a claim is checkable.
- Penn State Extension — Mulching Landscape TreesIndependent practical guidance on mulch depth and keeping mulch clear of the trunk.
- Penn State Extension — Using Composts to Improve Turf PerformancePublished surface-application volumes per unit area, used above as an independent cross-check on thin lawn applications.
- American Cement Association / Portland Cement Association — Applications of cementBackground on ready-mixed concrete, how it is batched and delivered, and how cement-based materials are compacted and cured.
These references support general background only. Product data, local requirements and site conditions take precedence over anything published here.
Limitations
Where this estimate stops being useful
Densities, product yields, packaging, compaction behaviour, site conditions and local requirements vary, and this site cannot see any of them. Estimates are planning aids for ordering conversations — not structural engineering, property surveying, code review or manufacturer instructions, which remain required where they apply. Confirm quantities with your supplier before purchase, and have a qualified professional confirm anything structural, drainage-related or permit-dependent.
The about page explains what the platform does and does not do, and the how it works page walks through the workflow end to end.