Work out how many plants a row will hold and how many seeds — and packets — you actually need to sow, once germination rate and a safety buffer are factored in.
Quick Facts
Method
Plants per row x rows, adjusted for germination rate plus a buffer
Seeds to sow = total plants / germination rate x (1 + buffer%).
Typical germination
70-95% for most fresh vegetable seed
Check the seed packet or your own germination test for an exact rate.
Results
Calculated
Plants per row
—
Row length ÷ in-row spacing
Total plants needed
—
Plants per row × number of rows
Seeds to sow
—
Adjusted for germination rate + buffer
Seed packets to buy
—
Seeds to sow ÷ seeds per packet
Ready
Enter your row plan and germination rate, then press Calculate.
Add this calculator to your website
How to use this calculator
Plan seed purchases for a vegetable bed by working from row length down to packets. Enter the length of a single row, how many identical rows you are planting, and the in-row spacing your crop needs; the calculator finds how many plants that layout holds. Add the seed's germination rate and a buffer for losses, and it finds how many seeds to sow — and how many packets to buy — to reliably fill every space.
The formula
Plants per row is row length divided by in-row spacing (both in the same units). Total plants needed is plants per row multiplied by the number of rows. Because not every seed sprouts, seeds to sow equals total plants divided by the germination rate (as a decimal), then increased by the buffer percentage to cover thinning, damping-off, and pests: seeds to sow = total plants ÷ germination rate × (1 + buffer%). Seed packets to buy is that seed count divided by the seeds printed on each packet, rounded up.
Interpreting the results
"Plants per row" and "Total plants needed" describe your finished bed if every seed you sow becomes a healthy plant. "Seeds to sow" is always higher than total plants needed — the gap is exactly the seed loss the germination rate and buffer are built to absorb. "Seed packets to buy" rounds that seed count up to whole packets so you do not come up short mid-planting.
Frequently Asked Questions
How do you calculate how many seeds to buy?
Divide your row length by the in-row plant spacing to get plants per row, multiply by the number of rows for total plants needed, then divide by the germination rate (as a decimal) and add a buffer percentage to cover thinning, pests, and uneven sprouting. Seeds to sow = total plants / germination rate x (1 + buffer). Round up to whole seeds and divide by seeds per packet to get packets to buy.
Why sow more seeds than the number of plants you want?
Germination rate is the percent of viable seeds that actually sprout under good conditions, and it is rarely 100%. A typical fresh vegetable seed germinates at 70-95%, so sowing exactly the number of plants you want would leave gaps. A buffer of 10-20% on top of the germination adjustment also covers seedlings lost to damping-off, slugs, or uneven emergence.
What is a typical germination rate for vegetable seeds?
Fresh, properly stored vegetable seed commonly germinates at 80-95% for crops like beans, squash, and peas, and 65-85% for finer seed like carrots, lettuce, and onions. Germination drops as seed ages; seed packets and germination tests give the most accurate figure for a specific batch.
How is in-row spacing different from row spacing?
In-row spacing is the distance between individual plants within the same row (used here to calculate plants per row). Row spacing is the distance between separate rows and does not change the seed count directly, but it does determine how many rows fit in a given bed width.