Gardening & Landscape Materials Estimation Guide
Calculating bulk soil and mulch cubic yards, seed rates, and plant spacing grids.
Landscape projects require estimating soil amendments, mulch, gravel, and seed. Buying materials in bulk by the cubic yard saves significant money compared to buying individual bags at garden centers, provided you measure depths and square footage accurately.
Where dividing by 324 converts square feet and inches of depth directly into cubic yards (since 27 cubic feet = 1 cubic yard).
Scenario: Covering flower beds totaling 450 square feet with a 3-inch layer of organic cedar mulch.
- Bed Area: 450 sq ft
- Depth: 3 inches
- Cubic Yards = (450 × 3) / 324 = 1,350 / 324
- Cubic Yards = 4.17 yards
- Add 10% settling factor = 4.17 × 1.10 = 4.58 yards
- Never mound mulch directly against tree trunks ("mulch volcanoes"); leave a 3-inch gap around bark to prevent fungal rot.
- One cubic yard of soil or mulch fills approximately 13.5 standard two-cubic-foot bags or 9 three-cubic-foot bags.
- When calculating vegetable garden spacing, use hexagonal spacing rather than square grids to fit 15% more plants per bed.
- Loamy garden soil settles 15% to 20% after initial installation and thorough watering.
Put the formulas above into practice with these free tools:
Raised Bed Soil Calculator
Soil volume and number of bags needed to fill a raised bed.
Plant Spacing Calculator
How many plants fit in a bed at a given spacing.
Lawn Seed Calculator
How much grass seed you need for a new or overseeded lawn.
Fertilizer Application Calculator
How much fertilizer to spread to hit a nitrogen target.
Garden Watering Calculator
Weekly water volume for a garden bed or lawn.
Rainwater Harvesting Calculator
Water you can collect from a roof and the barrels to store it.
Seed Starting Calculator
How many seeds to sow to end up with the plants you want.
Vegetable Garden Size Calculator
How big a vegetable garden you need to feed your household.
Pot Soil Volume Calculator
Potting mix needed to fill round planters and containers.
Growing Degree Days Calculator
Heat accumulation used to time planting and harvest.
How deep should garden mulch be applied?
A depth of 2 to 3 inches is optimal for weed suppression and moisture retention; deeper than 4 inches can suffocate plant roots.
How do I calculate grass seed requirements for a new lawn?
Standard cool-season grass seed requires 6 to 8 pounds per 1,000 square feet for new lawns, and 3 to 4 pounds for overseeding.
How much does one cubic yard of soil weigh?
Dry topsoil weighs approximately 2,000 to 2,200 pounds (about 1 ton); damp soil can exceed 2,700 pounds.