Square foot garden calculator

How square foot gardening counts plants

The method, popularized by Mel Bartholomew’s book Square Foot Gardening, divides a shallow raised bed into a 1 ft grid. Instead of rows, each square gets a fixed number of plants based on how big the plant grows: 1 for large plants, 4 for medium, 9 for small, 16 for tiny ones. University of Wisconsin Extension class notes on the method use the seed-packet spacing to choose: a 12 in spacing means one plant per square, 6 in means four, and 4 in means nine. They also advise a frame no wider than 4 ft (2 ft if you can reach from only one side), 6–8 in deep, with 2–3 ft walkways between beds.

squares = length (ft) × width (ft), whole squares only
plants = squares@1 + 4 × squares@4 + 9 × squares@9 + 16 × squares@16
soil = length × width × depth

Soil for a square foot bed

The original method uses a shallow 6 in bed filled with "Mel’s Mix" — equal parts compost, peat moss (or coir) and vermiculite. Many gardeners go deeper, especially over poor ground. The calculator shows the fill volume at your chosen depth; use the raised bed soil calculator for bag counts and mix breakdowns.

The classic first bed is a 4 × 4: see how many plants fit in a 4×4 square foot garden for a worked plan. For ornamentals or anything not on the 1-4-9-16 grid, how many plants for a 10×10 bed at 12 inch spacing uses ordinary spacing instead.

Tips

• Put tall crops and trellises on the north side (in the northern hemisphere) so they don’t shade the rest.
• Replant a square as soon as it is harvested — that is where the method gets its productivity.
• A visible grid (wood lath or string) helps you stick to the spacing.
• Water at the base of the plants. A few beds need far less water than a row garden; how much water a 10×20 vegetable garden needs shows the weekly figure for a bigger plot.