About the Bulb Spacing Calculator
When you plant flowering bulbs — tulips, daffodils, crocus, alliums, hyacinths — the single biggest decision after choosing the variety is how far apart to space them. This calculator takes the area of your bed and the recommended center-to-center spacing and tells you two things: how many bulbs you need to fill the bed, and the planting density in bulbs per square foot. That lets you buy the right quantity before you dig, instead of running short or over-ordering.
The formula
The calculation assumes a square planting grid, where each bulb sits at the center of a square cell whose side length equals the spacing. The number of bulbs that fit in an area is:
Bulbs = Bed area ÷ (Spacing × Spacing), using consistent units.
Because spacing on bulb packages is usually given in inches while beds are measured in square feet, the tool converts internally: there are 144 square inches in one square foot, so the density is 144 ÷ spacing² bulbs per square foot when spacing is in inches. For example, at 6-inch spacing the density is 144 ÷ 36 = 4 bulbs per square foot, so a 15-square-foot bed needs 15 × 4 = 60 bulbs.
Why spacing matters
Spacing controls both the look and the health of the display. Too tight, and bulbs compete for water and nutrients, producing smaller blooms and encouraging fungal disease from poor airflow; the planting also gets crowded faster and needs dividing sooner. Too loose, and the bed looks sparse and weedy. A common horticultural rule of thumb is to space a bulb about three times its own width apart — so a 2-inch-wide tulip bulb goes roughly 5 to 6 inches apart.
Typical spacing reference points
- Crocus, grape hyacinth, snowdrops (small bulbs): about 3 inches apart (~16 per sq ft).
- Tulips, daffodils, hyacinths (medium bulbs): about 4 to 6 inches apart (~4 to 9 per sq ft).
- Large alliums, crown imperial (large bulbs): about 8 to 12 inches apart (~1 to 2.25 per sq ft).
These are center-to-center distances. For a natural, drift-style planting, use the looser end of the range; for a dense formal block of color, use the tighter end.