Seed Needs Calculator

To calculate seeds needed, first determine your garden's total plant capacity: multiply the number of rows (garden width ÷ row spacing + 1) by plants per row (garden length ÷ plant spacing + 1). Then divide the total plants by your expected germination rate (e.g., 80% = 0.80) to account for seeds that won't sprout. Finally, add a safety margin of 10-20% for thinning and unexpected losses. Our Seed Needs Calculator above does all this automatically.

Row spacing is the distance between adjacent rows in your garden bed — it determines how many rows you can fit across the width of your garden. Plant spacing (also called seed spacing or in-row spacing) is the distance between individual plants within a single row — it determines how many plants fit along the length of each row. Both are critical for ensuring proper air circulation, sunlight exposure, and nutrient access for healthy plant growth.

Germination rate is the percentage of seeds expected to successfully sprout under proper conditions. If your germination rate is 80% and you need 100 plants, you'll actually need to sow 125 seeds (100 ÷ 0.80 = 125). Most seed packets list the tested germination rate. Older seeds or improper storage can lower this rate, so it's wise to use a conservative estimate and always plant a few extra seeds per cell or hole.

Yes! We recommend a 10-20% safety margin for several reasons: (1) some seedlings will need thinning, (2) pests or diseases may claim a few plants, (3) weather events can damage young seedlings, and (4) you may want to select only the strongest seedlings to transplant. Extra seeds are inexpensive insurance for a successful harvest. Our calculator includes an adjustable "Extra Seeds" percentage in Advanced Settings.

The number of packets depends on your garden size, crop spacing requirements, and seeds per packet. For example, a 20×15 ft garden growing bush beans (row spacing 21", plant spacing 4") with 50 seeds per packet at 80% germination would need approximately 4-5 packets. Crops with tiny seeds like carrots or lettuce often come with 500+ seeds per packet — one packet may be plenty. Larger-seeded crops like squash or pumpkins may only have 10-25 seeds per packet, requiring multiple packs for larger gardens.

For raised beds, you can often use slightly tighter row spacing than traditional in-ground gardens because the soil is typically richer and better-draining. A good rule of thumb is to reduce row spacing by about 15-25% compared to standard recommendations. For example, if the standard row spacing for lettuce is 18 inches, in a raised bed you might use 14-15 inches. Always ensure adequate airflow to prevent fungal diseases.

A general rule is to plant seeds at a depth of 2-3 times their diameter. Tiny seeds like lettuce and carrots need only a light covering of soil (⅛–¼ inch), while larger seeds like beans and corn should be planted 1-2 inches deep. Always check the seed packet for specific recommendations, as planting too deep can prevent germination and planting too shallow can expose seeds to drying out. Refer to our Sowing Depth Reference table above for common crops.

Yes! For square foot gardening, set your row spacing equal to your plant spacing (since plants are arranged in a grid pattern). For example, if you're planting lettuce at 4 plants per square foot, set both row spacing and plant spacing to 6 inches. The calculator will then give you an accurate count of how many plants fit in your total garden area using a grid layout rather than traditional rows.