Seed Calculator: How Many Seeds and Packets Do I Need?
Running out of seed halfway down a row is annoying; buying five packets you never use is wasteful. The right number depends on how many plants you want and how many seeds actually come up.
Runs in your browser. Nothing you enter is stored.
What this calculator does
Plan by rows or by plant numbers, enter the germination rate and packet size. The calculator gives the seeds to sow and packets to buy.
How to use the seed calculator
- Choose rows or a number of plants.
- Enter rows, length and final spacing, or the plants you want.
- Enter the germination rate from the packet.
- Set seeds per spot if you sow several and thin.
- Add spare seed for gaps and resowing.
How the calculation works
plants = rows × (floor(row length ÷ spacing) + 1) seeds = ceil(plants × seeds per spot ÷ germination × (1 + spare %)) packets = ceil(seeds ÷ seeds per packet)
Packets list minimum germination rates; fresh seed often does better.
Worked example
Three 3 m rows of carrots thinned to 5 cm give 183 plants. At 70% germination with 10% spare, sow 288 seeds: one packet of 500.
Assumptions and limitations
- Germination outdoors is often lower than on the packet.
- Small seeds are hard to sow singly; seed tape or pelleted seed helps.
- Seed counts per packet vary by brand.
Frequently asked questions
How many seeds should I plant per hole?
Usually 2–3 for larger seeds with uncertain germination, then thin to the strongest.
How many seeds are in a packet?
It varies widely: a carrot packet may hold 500–2,000 seeds, a squash packet 10–25.
How do I allow for germination?
Divide the plants you want by the germination rate: 100 plants at 80% needs 125 seeds.
How long do seeds stay viable?
Typically 1–5 years depending on crop and storage; onions and parsnips are short-lived.