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Seed Rate & Plant Population Calculator

Work out how many plants (and roughly how much seed) you need for a plot, from real row and in-row spacing figures for common vegetable crops — or your own custom spacing.

Plants needed15
Plants per sq ft0.15

How to measure your inputs

  • Plot area: measure or estimate your growing area in square feet.
  • Custom spacing: use your seed packet or a local extension guide's figures if your crop or variety isn't in the presets.

Methodology

Standard horticultural density formula: plants per sq ft = 1 ÷ (row spacing × in-row spacing, both in feet). Preset spacings are midpoints of the ranges published by University of Maine Cooperative Extension's vegetable planting chart.

Getting plant spacing right before you sow

Why row spacing and in-row spacing are different decisions

Row spacing is largely about access — room to walk, weed, and harvest between rows. In-row spacing is about competition — how much room each plant has for roots, light, and airflow. Crowding in-row spacing tends to hurt yield and disease resistance faster than tight row spacing does, which is why the two numbers are set independently rather than as one combined "spacing" figure.

Where these preset spacings come from

The crop presets here are midpoints of the ranges published by University of Maine Cooperative Extension’s vegetable planting chart — a real extension-service reference, not a generic average. Your specific variety, soil, and climate can shift the ideal spacing somewhat; the presets are a solid, defensible starting point, not a hard rule.

When to go custom instead of a preset

Use the custom spacing option when growing a variety with unusual vigor (compact/dwarf or heirloom sprawling types often differ significantly from the standard spacing for their species), or when following a specific trellising or intensive-spacing method that intentionally departs from traditional row spacing.

Frequently asked questions

What happens if I plant too closely?

Crowded plants compete for light, water, and nutrients, which typically reduces yield per plant and increases disease pressure from poor airflow — sometimes total yield per area still goes up despite smaller individual plants, but not always, and disease risk is a real cost either way.

Does plant spacing change between raised beds and traditional rows?

Often yes — raised-bed and intensive/biointensive methods frequently use tighter spacing than traditional single-row field spacing, since beds are worked from the side rather than needing space for equipment or foot traffic between every row. The presets here reflect traditional row spacing; intensive methods may support closer spacing.

How much seed do I need, not just how many plants?

This calculator gives plant count, not seed count — for direct-sown crops, account for germination rate (typically sow 10-20% more seed than your target plant count to allow for less-than-100% germination) or plan to thin after germination.

Why isn't my crop in the preset list?

Use the custom spacing option with figures from your seed packet, a local extension office, or a specific variety’s supplier data — the calculation logic is identical regardless of which spacing numbers you use.