Vegetable Seed Calculator (seed or transplants per row length, 38 crops)

Understanding the vegetable seed calculator — concept and principle

This calculator tells you how much seed, or how many transplants, onion sets or sweet-potato slips, to buy for the rows you plan to plant. It covers 38 vegetables and scales a university extension planting guide to your row length. Use it when ordering seed for a home or community garden.

How it is calculated

Amount = guide amount per 100 ft × (row length × rows ÷ 100 ft)

• Seed amounts are in ounces in the guide and converted to grams (1 oz = 28.35 g).
• Where the guide gives a range, such as sweet corn 3–4 oz or tomatoes 35–65 plants, both ends are shown and the larger is used for the amount to buy.
• Plant counts are rounded up to whole plants.
• In metric mode, metres are converted to feet first (1 ft = 0.3048 m).
• In-row spacing is shown in centimetres when the guide gives a single spacing.

The principle

Seed needs grow in direct proportion to row length: twice the row needs twice the seed. Extension guides tabulate the amount for a standard 100 ft row, so any garden is a simple fraction or multiple of that. The guide amounts already allow for thinning, which is why seed amounts are larger than the final number of plants. For transplanted crops the guide gives a range because spacing can be closer or wider depending on the variety and how you train the plants.

Worked example

Default inputs: tomatoes (transplants), US feet, 2 rows of 25 ft.

1. Total row length = 25 × 2 = 50 ft, or 50 × 0.3048 = 15.2 m.
2. Scale = 50 ÷ 100 = 0.5.
3. Plants = 35 × 0.5 = 17.5 and 65 × 0.5 = 32.5, rounded up to 18–33 plants.
4. Buy 33 transplants (the larger number); no seed weight applies, and spacing is a range (18–36 in), so no single spacing is shown.

How to read the result

The lower number suits wider spacing or large, sprawling varieties; the higher one suits staked or caged plants set closer. For seed crops, buy the amount shown or the nearest packet size above it, and check the packet, because seed size differs between varieties. Leftover seed of many crops keeps for another season if stored cool and dry.

Common mistakes

• Using the length of the bed instead of the total of all rows.
• Mixing feet and metres.
• Expecting every seed to grow; the guide allows for thinning and losses.
• Planting transplants at the closest spacing without support.

Frequently asked questions

How many tomato plants per 100 ft of row?

The guide gives 35–65 transplants per 100 ft.

How much sweet corn seed do I need?

About 3–4 oz per 100 ft of row in the guide, roughly 85–113 g.

Can I use the result for raised beds?

Yes, enter each bed's planting rows as row length.

Sources: Mississippi State University Extension, "Planting Guide" (Lawn and Garden: Vegetable Gardens)