Bulb Spacing Calculator (how many tulip, daffodil & crocus bulbs, and how deep)

Understanding the bulb spacing calculator — concept and principle

This calculator works out how many spring-flowering bulbs such as tulips, daffodils or crocuses you need for a bed, how far apart to plant them and how deep. It uses spacing and depth guidance from Cornell Cooperative Extension.

Area ÷ space per bulb: with the default inputs the result is 73 bulbs (plant 13 cm deep).

How it is calculated

Area per bulb = spacing² (square grid) or spacing² × √3 ÷ 2 (triangular grid, about 13% less)

Bulbs = bed area ÷ area per bulb, rounded up

Presets: tulips and daffodils about 5 in (13 cm) deep and 8 in (20 cm) apart; small bulbs about 2 in deep and 2–4 in apart

Custom bulbs: depth of soil above the bulb ≈ 2 × bulb diameter

1 in = 2.54 cm; 1 ft² = 0.0929 m²

The principle

Each bulb needs room for its roots and leaves, so it is given a square (or, in an offset pattern, a slightly smaller hexagonal) patch of soil. Dividing the bed area by the patch area gives the number of bulbs. Planting depth protects bulbs from frost and drying and helps the stems stand; the rule of thumb is soil about twice the bulb's diameter above it.

Worked example

Default inputs: 3 m², tulips, square grid.

Spacing = 8 in = 20.3 cm; area per bulb = 0.2032² = 0.0413 m².
Bulbs = 3 ÷ 0.0413 = 72.7 → 73.
Depth = 5 in = 13 cm to the top of the bulb.
Density = 24.2 per m² = 2.3 per ft².

Each point is the calculator re-run with only “Bed area” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Bed area	Bulbs needed
0.75	19
1.5	37
2.25	55
3	73
3.75	91
4.5	109
6	146

How to read the result

Closer spacing gives a fuller display in the first year; wider spacing leaves room for bulbs to multiply. For a natural drift of small bulbs, Cornell suggests about 20 per square foot. Plant in autumn before the ground freezes, in well-drained soil.

Common mistakes

Planting too shallow, so bulbs dry out or are dug up by animals.
Measuring depth to the bottom instead of the top of the bulb, or the other way round.
Planting in soggy soil, where bulbs rot.

Keep in mind: Some bulbs, such as daffodils, are toxic if eaten by pets or people; store and plant them out of reach.

Frequently asked questions

How deep do I plant tulips?

About 5 in (13 cm) of soil above the bulb.

How far apart should tulips be?

About 8 in (20 cm) in the Cornell guide; closer for a dense display.

Does the triangular grid fit more bulbs?

Yes, about 15% more for the same spacing.

Sources: Cornell Cooperative Extension, Lee RE, Kozlowski RE, "The Culture of Spring-Flowering Bulbs" (rev. 2008)

Checked 9 Nov 2026. Cornell Cooperative Extension, R. E. Lee & R. E. Kozlowski, “The Culture of Spring-Flowering Bulbs” (rev. T. Kowalsick, 2008): depths and spacings for tulips, narcissus and small bulbs; soil above the bulb about twice its diameter; about 20 small bulbs per ft² for naturalising.

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