Seeds & Germination

Seed Packet Planner

Work out exactly how many seed packets to buy before planting. Enter the seeds per packet, your plant spacing, bed size, and germination rate to get the number of packets, seeds to sow, and seeds left over for storage.

Check your seed packet for this number

Most vegetable seeds have a 75–95% germination rate. Older seeds germinate less reliably.

How to use the seed packet calculator

Buying seeds without a plan usually means one of two outcomes: you run short halfway through planting and leave gaps in the bed, or you spend money on packets you never open. This calculator settles the question before you reach the checkout. Enter how many seeds are in a packet, the spacing you want between plants, the length and width of your bed, and the germination rate printed on the packet. In return you get the number of plants your bed holds, how many seeds to sow once germination losses are factored in, the number of packets to buy, and how many seeds you will have left to store.

Why germination rate matters

Germination rate is the single biggest reason seed math trips people up. A packet rarely sprouts every seed, so the number you sow has to be larger than the number of plants you want to end up with. If you need 32 plants and your seed germinates at 85%, sowing exactly 32 seeds would, on average, leave you with around 27 plants. Dividing the plant count by the germination rate (32 ÷ 0.85 ≈ 38 seeds) builds in the right cushion. Fresh seed from a reputable supplier is usually in the 75–95% range; seed that is several years old or stored in heat and humidity can fall well below that, which is why testing a small batch on a damp paper towel is worthwhile before you commit a whole bed to it.

Spacing, bed size, and plant count

The calculator turns your spacing into a simple grid. It converts the spacing from inches to feet, then divides the bed length and width by that figure and rounds each down to a whole number, because a partial plant cannot grow at the edge of a bed. Multiplying the two gives the plant count. Use the center-to-center spacing from the seed packet — for example, "thin to 6 inches apart" — rather than the distance between leaves. For intensive or square-foot style planting you can enter a tighter spacing, but avoid crowding plants so closely that airflow drops and disease pressure climbs.

Sowing and storing the surplus

A reliable field technique is to sow two seeds per spot and thin to the strongest seedling once they are up, which fills the bed evenly without bare patches. Whatever seed is left over is not wasted: stored in an airtight container somewhere cool, dark, and dry, most vegetable seed stays viable for two to five years. Label each packet with the year and keep a silica gel or rice desiccant in the container to fend off moisture. Saved seed is ideal for succession sowing through the season and for replacing the occasional plant lost to weather or pests, so the few extra seeds the calculator leaves over often turn into next year's head start.

Frequently Asked Questions

How many seeds are in a seed packet?

It varies widely by crop and supplier. A packet of large seeds like beans, peas, or squash may hold 15 to 50 seeds, while small seeds such as lettuce, carrots, or basil can hold several hundred. The seed count is usually printed on the back of the packet, often as a weight or an approximate number — enter that figure into the calculator for the most accurate result.

Why do I need to sow more seeds than the number of plants I want?

No seed packet germinates at 100%. If a packet lists an 85% germination rate, then on average only 85 of every 100 seeds sprout. To end up with the number of plants your bed needs, you sow extra seeds to cover the ones that fail. The calculator divides your plant count by the germination rate to find how many seeds to sow.

What is a germination rate and where do I find it?

Germination rate is the percentage of seeds expected to sprout under good conditions. Reputable seed companies test each lot and print the rate and a "packed for" year on the packet. Most fresh vegetable seed falls between 75% and 95%. If no rate is listed, 85% is a reasonable default for fresh, properly stored seed.

Should I really sow two seeds per spot?

For direct-sown crops, planting two seeds per hole or station is a common insurance policy against gaps. If both sprout, snip the weaker seedling at soil level with scissors rather than pulling it, which protects the roots of the one you keep. This gives you a full bed without the bare patches that come from single-seed sowing.

How long do leftover seeds last in storage?

Stored cool, dark, and dry, most vegetable seeds stay viable for two to five years, though it depends on the species. Onions, parsnips, and leeks are short-lived (about one year), while tomatoes, cucumbers, and brassicas can last four years or more. Keep leftover seed in an airtight container with a desiccant packet and label it with the year.

Should I round the number of packets up or down?

Always round up — and this calculator does. Because you cannot buy a fraction of a packet, it uses the ceiling of the seeds-needed divided by the packet size, so you never come up short mid-planting. Any surplus shows as "seeds leftover for storage," which you can save for succession sowings or next season.

More Tools to Explore

Plant Spacing Calculator How many plants fit in your bed Open tool → Square Foot Garden Planner Plants per square foot, any bed size Open tool → Seed Starting Calculator When to start seeds indoors Open tool →

GardenCalc Editorial Team

Horticulture Writers & Master Gardeners

Our calculators and guides are written and fact-checked by gardeners with hands-on experience in vegetable production, soil management, and home landscaping.