Spacing is on the plant tag for a reason
Plant count is bed area divided by the square each plant needs at maturity: a 12-inch spacing gives one plant per square foot. Cramming annuals together looks full on day one and becomes a fungal problem by July — the tag's mature spacing is the number to enter, not the size the plant is today.
Stagger for fullness
Rows planted in a grid show gaps; offsetting alternate rows (triangular spacing) covers the same area with the same plants and reads much fuller. For borders, run the math per plant type separately, then add — mixes need their own counts.
Sources and standards
Where these figures come from
Every formula on this page is implemented from the published reference material below. Where a value depends on a regional code, the calculator lets you override it rather than assuming one jurisdiction.
- USDA Natural Resources Conservation Service — soil texture, bulk density and seeding rate guidance.
- US Geological Survey — mineral commodity data and aggregate density references.
- National Stone, Sand & Gravel Association — aggregate grading and product specification references.
Figures, formulas and reference tables last verified: 19 September 2026.