This seed calculator estimates how many seeds you need to sow an area or row at a given spacing, allowing for germination rate so you sow enough to reach your target number of plants. It takes the guesswork out of ordering seed and planning a sowing.
From spacing to seed count
The number of plants an area supports comes from the spacing between plants and between rows: closer spacing means more plants but more competition. The calculator divides the area (or row length) by the spacing to find the plant positions, then works back to how many seeds to sow. Because not every seed germinates, it divides by the germination rate so you sow a surplus and still hit your target.
Sowing method matters too. Direct sowing into the ground usually wastes more seed than starting in modules and transplanting, and some growers sow two or three seeds per station and thin to the strongest. Building the germination rate and a thinning allowance into the figure means you order enough without huge over-purchase.
Why germination rate counts
Seed packets quote a germination percentage, and it falls as seed ages. If only 80% of seeds sprout, you must sow 25% more than your target plant count to compensate. Ignoring this is the usual reason a row comes up patchy and short of the plants you planned for.
You want 100 lettuce plants and the seed has an 80% germination rate.
- Target plants = 100.
- Account for germination: seeds = 100 ÷ 0.80.
- Seeds to sow = 125.
Sow about 125 seeds to end up with roughly 100 plants at 80% germination.
