Garden Planning Calculator

Calculate how many plants fit, seeds needed, soil, and fertilizer for your garden

Length

Width

Unit

Plant Type

Plant Spacing (inches)

Typical: herbs 6–12in, flowers 12–18in, vegetables 12–24in

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Quick summary

Enter your garden dimensions, plant type, and spacing to calculate how many plants fit, seeds needed (with 20% germination buffer), soil cubic feet for a 6-inch depth, and fertilizer requirements.

Reviewed by Simple Calculators TeamLast reviewed July 10, 2026

How to use this calculator

Enter the inputs requested by the calculator.
Choose the units or options that match your situation and review the assumptions.
Run or update the calculation to see the result.
Review the result, breakdown, and formulas shown on the page.
Check the inputs, units, dates, and limitations before saving or sharing the result.

Garden Planning Formulas

Number of Plants

\text{Plants} = \frac{\text{Garden Area (sq ft)}}{(\text{Spacing (ft)})^2}

Garden Area: Length × Width in sq ft
Spacing (ft): Plant spacing converted from inches to feet

Worked example

100 sq ft garden, 18 inch spacing

Given: Area = 100 sq ft
Spacing = 18 inches = 1.5 ft
Calculation: $\text{Plants} = \frac{100}{1.5^2} = \frac{100}{2.25}$
Result: 44 plants

Soil Volume

\text{Soil (cu ft)} = \text{Area (sq ft)} \times \frac{\text{Depth (in)}}{12}

Depth: Recommended soil depth: 6 inches

Worked example

100 sq ft garden, 6 inch depth

Given: Area = 100 sq ft
Depth = 6 in
Calculation: $100 \times \frac{6}{12} = 100 \times 0.5$
Result: 50 cubic feet of soil

Frequently asked questions

What spacing should I use for vegetables?

Common vegetable spacings: tomatoes 24–36in, peppers 18–24in, lettuce 6–12in, carrots 2–4in, zucchini 24–36in. Check seed packets for exact recommendations.

Why add a 20% buffer for seeds?

Not all seeds germinate — typical germination rates are 70–90%. A 20% buffer ensures you have enough plants even if some seeds fail to sprout.

How deep should raised bed soil be?

Most vegetables need 6–12 inches of soil depth. Leafy greens and herbs do well with 6 inches; root vegetables (carrots, potatoes) need 12+ inches.

Key terms

Square Foot Gardening: A method of growing plants in closely spaced grids to maximize yield per square foot.
Germination Rate: The percentage of seeds that will successfully sprout under ideal conditions.
Cubic Foot: A volume unit used for soil and mulch — 1 cubic foot = a 12×12×12 inch cube.

Methodology, sources & limitations

This page shows the formula, assumptions, and limitations used for this estimate. Rates, thresholds, and other time-sensitive inputs can change, so verify them against the relevant official source before relying on a result.

For our review approach and the primary sources we consult, see the methodology and source policy. If you spot an outdated figure or formula, please contact us with a correction.

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