Seed Quantity Calculator
Work out how many seeds to sow and how much seed to buy, in ounces, grams, and packets, from bed feet, spacing, germination rate, and a buffer for losses.
Free · no account · works on mobile · embeddable
Best for market gardeners, CSA growers, and homesteaders ordering seed for the season. Updated .
Crop and planting
Seed to sow and buy
Plants = bed feet × 12 ÷ in-row inches × rows. Seeds to sow = plants × seeds per plant ÷ germination × (1 + extra). Weight = seeds ÷ seeds per ounce. Seed counts per ounce vary by variety and lot, so treat the weight as a planning figure and check the catalog.
About the seed quantity calculator
Seed orders are usually guessed from last year's leftovers, and the guess is wrong in both directions: too little carrot seed in April, three unopened packets of squash in the drawer. This calculator starts from the bed feet you will plant, the rows per bed, and the in-row spacing to find how many plants you want, then adds seeds per plant, germination rate, and a buffer for losses to give the number of seeds to sow. Dividing by seeds per ounce turns that into a weight in ounces and grams, rounded up to a quarter ounce to buy, and into packets at the count you enter.
It is for anyone planning a season's seed order: market gardens working from a crop plan, CSA farms scaling a mix, and serious home growers who would rather buy by the ounce than by the packet.
From bed feet to plants to seeds
Plants wanted is bed feet x 12 / in-row spacing in inches x rows per bed. A 100 ft bed with three rows of carrots at 2 in spacing holds 1,800 plants. Seeds to sow multiplies by the seeds you drop per final plant (1 for a transplant cell, 2 or 3 for a thinned direct-sown row), divides by the germination rate on the packet or lot test, and adds your extra percentage for damping off, pests, spills, and a possible second sowing.
The crop presets take in-row spacing from University of Georgia Extension's planting chart and seeds per ounce from University of Maryland Extension's seed-size table, using the low end of the range so the estimate leans toward buying slightly more. Every preset is editable; the best figures are the ones printed in your own seed catalog for the variety you are ordering.
Ounces, grams, and packets
Seed is sold by count in packets and by weight in bulk, and catalogs often quote both. The calculator shows the weight needed in ounces and grams, then rounds up to the next quarter ounce, which is the smallest bulk unit many suppliers sell. The packet count uses the seeds-per-packet figure you enter, because packet sizes range from 25 seeds of a hybrid tomato to several thousand carrot seeds. Compare the price per seed of bulk and packets before deciding which to buy.
Worked example: 200 bed feet of carrots
200 bed feet with 3 rows per bed at 2 in spacing is 600 row feet and 1,200 plants per row, so 3,600 plants wanted. Sowing 3 seeds per final plant means 10,800 seeds before losses; at 75% germination with 10% extra that is 15,840 seeds to sow, or 79.2 seeds per bed foot. At 18,750 carrot seeds per ounce the order is 0.84 oz (23.9 g): buy 1 oz in bulk, or 32 packets of 500 seeds.
Sources
- University of Maryland Extension, Table G-1. Vegetable seed sizes. Seeds per ounce or per pound by crop, for example 300,000 to 400,000 carrot seeds per pound, 10,000 to 11,400 fresh-market tomato seeds per ounce, and 4,000 to 4,700 pepper seeds per ounce. Accessed Sep 4, 2026.
- University of Georgia Extension, Growing vegetables organically (Bulletin 1011), Table 7 planting chart. Between-row and in-row spacing plus seed or plants per 100 ft by crop, for example carrots 18 to 36 in by 2 to 3 in and tomatoes 48 in by 24 in. Accessed Sep 4, 2026.
This calculator gives planning estimates from the numbers you enter. It is not accounting, tax, veterinary, or legal advice. Replace the defaults with your own farm records whenever you have them.
Frequently asked questions
How much seed do I need per 100 feet of row?
It depends on spacing and seed size. Extension planting charts list about a half ounce of carrot seed, one ounce of beet seed, a half pound of bush bean seed, and 50 to 100 transplants of tomato or cabbage per 100 ft of row. The calculator gives the figure for your spacing and germination rate rather than an average.
How many seeds are in an ounce?
Roughly 100 snap beans, 1,500 beets, 4,000 peppers, 8,500 broccoli or cabbage, 10,000 tomatoes, 18,750 or more carrots, and 25,000 leaf lettuce seeds per ounce, using the low end of University of Maryland Extension's seed-size table. Variety and seed lot change these counts, so use the catalog figure when you have it.
Should I add extra seed for germination?
Yes. Divide by the germination rate on the packet: 100 plants at 80% germination need 125 seeds before any other losses. Then add a buffer, commonly 10 to 25%, for damping off, pests, poor stands, and a second sowing. For direct-sown crops you thin, sow 2 to 3 seeds per final plant on top of that.
How many rows per bed should I plan?
Common market-garden layouts on a 30 in bed are one row of tomatoes or squash, two rows of brassicas or lettuce, three rows of carrots or beets, and four or more rows of salad mix or radishes. Enter your own layout; the calculator multiplies plants per row by rows per bed.
Does this work for transplants started in trays?
Yes. Set seeds per final plant to 1 (or 1.2 to fill blank cells), enter the tray germination rate, and the result is the seed count and weight for the number of transplants you need. Use the seed starting date calculator to decide when to sow the trays.
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