Square Foot Gardening Calculator
Plan a square foot garden: how many squares your raised bed has, how many plants of each vegetable go in a square (1, 4, 9 or 16) and how many seeds or seedlings to buy — metric or feet.
How it works
squares = ⌊length ÷ 30 cm⌋ × ⌊width ÷ 30 cm⌋ (or 1 ft squares) · plants = squares × plants per square (1, 2, 4, 8, 9 or 16) · spacing = square side ÷ √(plants per square)
Square foot gardening, popularized by Mel Bartholomew, divides a raised bed into a grid of 1 ft (30 cm) squares and plants each square at a fixed density instead of in rows: 1 large plant (tomato, pepper, broccoli, cabbage), 2 trellised cucumbers, 4 medium plants (lettuce, chard, strawberries, herbs), 8 trellised peas or pole beans, 9 small plants (beets, spinach, bush beans) or 16 tiny ones (carrots, radishes, green onions). The method uses roughly 80% less space and less water than row gardening. Sow 1–3 seeds per hole and thin to one plant.
Worked example
A 120 × 120 cm bed has 4 × 4 = 16 squares of 30 cm. Leaf lettuce goes 4 per square, so the bed holds 16 × 4 = 64 plants, about 15.0 cm apart; sowing 2 seeds per hole takes 128 seeds.
Sources: Mel Bartholomew Square Foot Gardening Foundation · University of Maryland Extension — Square foot gardening
Frequently asked questions
How many plants per square foot?
Large plants such as tomatoes, peppers, broccoli and cabbage: 1. Lettuce, chard, strawberries and most herbs: 4. Beets, spinach, bush beans and garlic: 9. Carrots, radishes and green onions: 16. Trellised peas and pole beans: 8.
How big should a square foot garden bed be?
The classic bed is 4 × 4 ft (about 120 × 120 cm), giving 16 squares that you can reach from every side without stepping on the soil. Beds against a wall should be no deeper than 2–3 ft.
Can I grow squash or melons in a square foot garden?
Yes, but they need space: a bush zucchini or winter squash takes about 3 × 3 squares (9 squares), and melons are grown on a trellis at 1–2 per square.
What soil do I use?
Bartholomew’s “Mel’s Mix” is one-third compost, one-third peat moss or coco coir and one-third coarse vermiculite, about 15 cm (6″) deep. Use the raised bed soil calculator for the volume.
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This calculator is for educational purposes. Double-check important results before acting on them.