Guide
How many tomato seeds for a 4×8 bed?
Work from plant count and germination, then buy only the packet shortfall after leftover seeds.
A common 4×8 raised bed holds about four determinate tomato plants with cages, or six if you accept tighter spacing. Decide the plant count first — that is demand.
If your packet lists ~30 seeds and germination is 90%, usable seeds per pack are about 27. Four plants need four usable seedlings after germ loss, so you sow a few extras but still often need less than one full retail pack when you already have leftovers.
Example PlantIt trusts: 10 desired plants, 50 seeds/pack, 100% germ, half a pack on hand → 25 usable seeds available → 0 packets to buy. Forty plants with the same half pack leave 15 uncovered → buy 1 retail packet.
Use the public calculator with your packet size, then sign up to attach the same math to a real bed layout and shopping list.