Seed Spacing Calculator

How to use the seed spacing calculator

Spacing is one of those details that looks fussy and turns out to matter enormously. Seeds sown too closely compete for light, water and nutrients, and the result is a row of thin, weak plants that yield less than a properly spaced row half as long. Seeds sown too far apart waste space you could have used. This calculator does the simple arithmetic — row length divided by spacing — and adds the one thing most people forget: not every seed germinates, so it suggests sowing about 20% extra and thinning to the final spacing later.

Why the calculator uses the closer spacing

Every crop in our database carries a spacing range, for example 2–3 inches for carrots or 24–36 inches for tomatoes. The range exists because spacing depends on variety, soil fertility and how you grow: a vigorous variety in rich soil needs the wider end, a compact variety in a small bed can take the closer end. This calculator defaults to the closer end of the range, which gives you the maximum number of plants that can fit without crowding. If you are growing a large variety, or your soil is very fertile and plants grow big, use the custom spacing box to widen it — the seed count will drop, and that is the point. Better to grow eight strong plants than twenty weak ones.

Sow thick, thin later

The standard practice for direct-sown crops is to sow more thickly than the final spacing and then thin. Carrots are the classic example: sow the tiny seeds about an inch apart, then thin to 2–3 inches once the seedlings are a couple of inches tall. Thinning feels wasteful, but it is what makes the remaining plants grow to full size — and the thinnings of lettuce, spinach and beetroot are edible as baby leaves, so nothing is truly wasted. Thin on a calm evening, water afterwards, and thin in stages rather than all at once, so you can keep the strongest seedlings. For crops that hate root disturbance — carrots, parsnips, beans, peas — sow at final spacing where you can, and handle thinnings gently.

The 20% extra in the result is a planning allowance, not a rule. Fresh seed from a reputable supplier often germinates at 85–95%, while old seed stored badly may manage only half that. If you are using old seed, run a germination test first — ten seeds on damp kitchen paper, kept warm for a week — and adjust the allowance to match what actually sprouts. And remember that spacing in the packet is a guide for the variety it describes; dwarf and compact varieties can be planted closer, sprawling varieties need more room, and the soil you are growing in matters as much as the numbers.

Rows, beds and blocks

The calculator works in rows because that is how most people plant, but spacing works the same way in beds and blocks. In a raised bed, plants are often spaced in a grid rather than rows, which uses space more efficiently — a 4×4 foot bed holds more lettuce in a grid than in rows with paths between them. Row spacing (the distance between rows) matters for access: you need room to walk, weed and harvest without stepping on the bed. In a square-foot garden the same numbers apply in a different form — plants are grouped by how many fit in one square foot — and the spacing ranges in our database are the source for that too.

Related tools: the Plant Spacing Calculator works the same maths out for beds and transplanted plants, the Square-Foot Garden Planner lays out a whole bed, and the Seed Viability Checker tells you whether old seed is worth sowing at all. For sowing dates, see the Seed-Starting Calculator.