How We Calculate Volume and Round Purchases

1. Find the area

For each rectangular bed, multiply length by width. We convert feet and inches to feet first, then add the areas together. Metric lengths are converted to feet for the calculation.

Example: two garden beds

12 ft × 6 ft = 72 ft². An 8 ft × 4 ft bed adds 32 ft². Total: 104 ft².

2. Add depth and extra

Depth is entered in inches (or centimeters when using metric input). Divide inches by 12 to get feet, then multiply by total area. The extra percentage is a user-controlled allowance for small measurement differences and uneven ground. It is an estimate, not a universal requirement.

For 104 ft² at 3 in: 104 × 3 ÷ 12 = 26 ft³. With 10% extra: 26 × 1.10 = 28.6 ft³. Divide by 27 for cubic yards: 1.059 yd³.

3. Round to what you can actually buy

Divide the needed cubic feet by the size printed on the bag. Always round up to a whole bag. With 2 ft³ bags, 28.6 ÷ 2 = 14.3, so the shopping list says 15 bags.

For bulk, apply the supplier's minimum order and increment. If a supplier sells by the half yard, 1.059 yd³ rounds up to 1.5 yd³. A higher minimum could raise that purchase amount.

4. Compare your costs

Bag cost is whole bags × price per bag. Bulk cost is orderable cubic yards × price per cubic yard + delivery. The displayed difference uses these purchase totals, including unused material caused by rounding. Taxes, pickup costs, and special fees are not included unless you include them in your entered prices.

Where estimates can differ from reality

Real beds are rarely perfect rectangles. Product labels, compaction, settling, slopes, and supplier measurement practices can affect the amount used. Measure carefully and confirm the supplier's rules before ordering. The calculator is intended for planning a purchase, not a guaranteed installed volume.