Calculation Methodology

This page documents exactly how our calculators work, so you can verify any number by hand. Our guiding rule: unit conversions are exact mathematics; material quantities are planning estimates — and the site always tells you which is which.

Area formulas

Rectangle

Area = length × width

Circle

Area = π × (diameter ÷ 2)²

Triangle

Area = (base × height) ÷ 2

Custom

You enter the square footage directly

Irregular beds are handled by splitting them into several sections and letting the calculator combine them — total volume is the sum of every section's volume.

Volume formulas

Volume is a simple prism: depth multiplied across the area, with depth in inches divided by 12 to keep units consistent:

• Cubic feet = area (sq ft) × depth (in) ÷ 12
• Cubic yards = cubic feet ÷ 27 (one yard³ = 3 × 3 × 3 feet)

Unit conversions (exact)

• 12 inches = 1 foot; 3 feet = 1 yard
• 27 cubic feet = 1 cubic yard; 9 sq ft = 1 sq yd
• 2,000 pounds = 1 US short ton (the only ton we show)
• 1 foot = 0.3048 metre exactly (international foot); 1 inch = 2.54 cm exactly
• Metric equivalents are computed from those exact definitions — never rounded "≈" constants

Waste allowance

The waste allowance — a user-adjustable percentage that defaults to 10 % and can be set to 0 — covers spillage, compaction and small measurement errors. It is applied once, to the combined total: adjusted volume = base volume × (1 + waste ÷ 100). We show the base and adjusted quantities separately, so you always see exactly what the allowance added.

Package rounding

Bag counts are computed as adjusted cubic feet ÷ bag volume, then always rounded up to a whole bag — you cannot order part of a bag. Bag volume always comes from your selection or entry (1, 1.5, 2, 2.5, 3 cubic feet or a custom value), because manufacturers package the same product in different volumes.

Density and weight assumptions

Weight honestly depends on the specific product and its condition — moisture, grading, and supplier variation matter. Where a weight estimate is offered (pea gravel), it is shown as a range derived from a sourced density interval, and you can enter your supplier's density for a precise figure. When no reliable density source is published, the tool omits the weight entirely rather than show a fabricated number. Current source records, including URL and review date, live in the site's public material-configuration file: src/config/materials.ts.

Material variation

A yard of delivered mulch is not a yard of bagged mulch: bag volumes are net, bulk loads can settle in transit, and delivered aggregates compact after spreading. That is why every result page ends with the disclaimer below, and why we show both bagged and bulk options when you supply prices for both.

Which calculator does what

• Mulch Calculator — Estimate mulch in cubic feet, cubic yards and bags for one or more garden beds.
• Pea Gravel Calculator — Calculate pea gravel volume, bag count, optional tonnage and cost for paths and driveways.
• Raised Bed Soil Calculator — Work out how much soil (and mix components) you need to fill your raised garden beds.