Methodology
How Groundwork Calculators Work
The tools turn measurements into planning estimates using ordinary geometry, explicit unit conversions, and clearly labeled assumptions. This page shows what is mathematical fact, what is a configurable planning choice, and what must be verified with a supplier.
Area: measure the footprint first
Rectangles use length × width. Circles use π × radius², where radius is half the diameter. Triangles use base × perpendicular height ÷ 2. Multi-area tools calculate each shape, add the included areas, and subtract exclusions such as a shed, patio, pond, or planting island.
An exclusion cannot create a negative project. For L-shaped or disconnected spaces, use several non-overlapping shapes and label them on a field sketch. Apply project allowance only after those areas have been combined.
Volume: area × installed depth
A surface measurement becomes volume only after depth is included. In Imperial calculations, inches are divided by 12 before being multiplied by square feet. Cubic feet are divided by 27 to produce cubic yards. In metric calculations, centimeters are divided by 100 before being multiplied by square meters.
Example
A 12 ft × 8 ft bed at 3 in deep is 96 sq ft × 0.25 ft = 24 cu ft, or 24 ÷ 27 = 0.89 cu yd before allowance.
Volume and weight are different
Volume describes the space a material occupies. Weight depends on density. Gravel, sand, soil, decorative stone, concrete, and asphalt do not share one density, and even one product can vary with gradation, void space, moisture, and compaction.
Where a calculator shows tons or tonnes, it multiplies volume by the representative density disclosed on that page. That is a planning conversion—not a scale ticket. A supplier's product-specific density, compacted coverage, or weigh-ticket practice should replace the generic value when available.
Allowance is not compaction
The default allowance is a user-adjustable buffer for measurement variation, trimming, small spills, fitting, or minor site irregularity. It is applied once to the combined project quantity. It does not assert that every project needs the same extra amount.
Compaction describes loose material consolidating into a denser installed layer. Because the relationship depends on the product, moisture, placement method, and equipment, Groundwork does not treat one allowance percentage as a universal compaction factor. For compacted layers, enter the required finished depth and ask the supplier for loose quantity or compacted coverage.
Bags, pieces, pallets, and rolls
A bag may be sold by weight but state a volume or mixed yield. Those are not interchangeable unless density or manufacturer yield is known. Concrete bag estimates use the selected package yield; sod uses the supplier coverage entered by the user; fabric calculations use roll dimensions and overlap.
Purchase quantities round upward to whole packages, pieces, pallets, or rolls because a fraction of a package is normally not purchasable. Manufacturer coverage and yield take priority over a generic option.
Rounding
Calculations retain their unrounded numeric values through area, conversion, allowance, and package math. The interface shortens decimal values for readability. Purchase quantities are then rounded upward. This avoids the compounding error that can occur when each bed or intermediate conversion is rounded independently.
Imperial and metric conversions
| Relationship | Used for |
|---|---|
| 12 inches = 1 foot | Imperial depth |
| 27 cubic feet = 1 cubic yard | Bulk volume |
| 100 centimeters = 1 meter | Metric depth |
| 1 meter = 3.28084 feet | Linear conversion |
| 1 cubic meter ≈ 35.3147 cubic feet | Volume conversion |
Conversion constants follow standard relationships summarized in the U.S. National Institute of Standards and Technology guidance on SI units and volume.
Estimates and limitations
- Supplier or manufacturer specifications should override generic density, coverage, package, and yield values.
- Site grade, soft soil, moisture, drainage, access, settling, and construction method can change quantities.
- The tools estimate material quantity; they do not select a structurally adequate section.
- Code-regulated, drainage-sensitive, load-bearing, or safety-critical work may require local requirements or qualified professional input.
Checking and correcting the tools
Formulas are kept in reusable calculation functions and checked with automated cases for mixed shapes, exclusions, unit conversions, fabric overlaps, concrete shapes, sod coverage, gravel layers, and paver layers. Calculator pages are reviewed when functionality or planning guidance changes.
If a result appears wrong, send the dimensions, unit system, selected options, expected result, and calculator URL through the contact form. Reports are used to reproduce and correct calculation or content errors.