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Plants per square foot calculator
Pick a crop and your bed size. This gives you the plants-per-square count, the total for the whole bed, and a visual of what one square looks like. Below it is the full spacing chart for 60+ crops.
Take 12 inches, divide by the crop's spacing requirement, round down to a whole number, then square it. Carrots need 3 inches: 12 ÷ 3 = 4, and 4 × 4 = 16 per square. Lettuce needs 6: 12 ÷ 6 = 2, and 2 × 2 = 4 per square. Anything needing more than 12 inches takes one or more whole squares to itself.
Why rounding down matters
A crop wanting 5-inch spacing gives 12 ÷ 5 = 2.4. You cannot plant 2.4 rows, so you round down to 2 and plant 4 per square at a real spacing of 6 inches. Rounding up to 3 would put them 4 inches apart, which is tighter than the crop wants. Erring generous is nearly always right — overcrowded plants compete for light and water and yield less than fewer, healthier ones.
The full square foot spacing chart
Every crop in the calculator, grouped by density. These are standard square foot gardening figures and the same ones Niwa applies automatically.
| Crop | Spacing | Per square | Notes |
|---|
Working out a whole bed
Multiply width by length in feet to get your number of squares — a 4×8 bed is 32. Then assign crops square by square rather than calculating one crop across the whole bed, because a real bed is a mix. A worked 4×4 example:
| Crop | Squares | Per square | Plants |
|---|---|---|---|
| Carrots | 2 | 16 | 32 |
| Radishes | 1 | 16 | 16 |
| Onions | 2 | 16 | 32 |
| Beetroot | 1 | 9 | 9 |
| Bush beans | 2 | 9 | 18 |
| Lettuce | 2 | 4 | 8 |
| Basil | 1 | 4 | 4 |
| Marigold | 1 | 4 | 4 |
| Peppers | 2 | 1 | 2 |
| Bush tomato | 2 | 1 | 2 |
| Total | 16 | — | 127 |
Three things the numbers don't tell you
Plan for August, not May
The chart assumes a mature plant. One courgette needs around nine square feet when it is fully grown, though the seedling looks lost in a single square in spring. Give big crops the room they will eventually need.
Height beats density
Perfect spacing is wasted if a trellis of cucumbers shades the lettuce all afternoon. Put tall crops on the north edge in the northern hemisphere, south in the southern.
Neighbours matter at this density
At twelve inches apart, root zones overlap almost entirely, so companion effects are real. Onions next to beans is the classic accidental clash. See how the app flags this →
Doing this for every square gets old fast. Niwa runs the same calculation for 200+ crops as you tap them onto a grid, prints the count on the cell, and then dates each one from your local frost. Free on iPhone.
Related
- Plant spacing calculator — for spacings that aren't standard SFG numbers
- Raised bed soil calculator — how much soil the bed needs
- The complete square foot gardening guide
Let the app do this for every square.
Niwa runs this same calculation for 200+ crops and prints the count on the grid.
Questions gardeners ask
How do you calculate plants per square foot?
Divide 12 inches by the crop's recommended spacing, round down to a whole number, then square the result. A crop needing 3-inch spacing gives 12 ÷ 3 = 4, and 4² = 16 plants per square foot. A crop needing 6 inches gives 12 ÷ 6 = 2, and 2² = 4 plants. Crops needing more than 12 inches take one or more whole squares each.
See it applied on a real gridHow many plants can I grow in a 4x4 raised bed?
A 4x4 bed has 16 square feet. Planted with a typical mix it usually holds 100 to 130 plants — a single square of carrots alone holds 16, while one bush tomato takes a whole square. Filling all 16 squares with 16-per-square crops would give 256 plants, but that would be all roots and no variety.
Plan a 4x4 bedIs Niwa free to use?
Yes. Niwa is free to download from the App Store, and the core planner — the garden grid, the plant library and the planting calendar — works without paying. Optional in-app purchases unlock additional features.
See it on the App StoreHow many plants fit in one square foot?
It depends on the crop's spacing requirement. A plant needing 3 inches fits 16 per square foot, 4 inches fits 9, 6 inches fits 4, and 12 inches fits 1. Large plants such as vining tomatoes or zucchini need more than one square each. Niwa works this out for you and prints the count straight onto the grid cell.
Plants per square foot calculatorCan Niwa plan a raised bed of any size?
Yes. You set the bed dimensions — 4×4, 4×8, 2×8 or a custom size — and Niwa draws the square foot grid to match. You can keep several beds and several gardens in the app at once and switch between them.
Raised bed plannerHow does Niwa know when I should plant?
Niwa uses your location to find your average last spring frost and first autumn frost, then works backwards from those dates for every crop in your bed. Each plant gets its own sow-indoors, transplant and harvest window on a month-by-month timeline, so the dates are yours rather than a generic zone table.
How the planting calendar worksDoes Niwa warn me about bad companion plants?
Yes. As you place plants on the grid, Niwa puts a green dot between neighbouring squares that benefit each other and a red dot between squares that are better kept apart, so you see the conflict while you are still planning.
Companion planting in NiwaHow much soil do I need to fill a raised bed?
Multiply length × width × depth in feet to get cubic feet, then divide by 27 for cubic yards. A 4×8 bed at 12 inches deep needs 32 cubic feet, roughly 1.2 cubic yards or sixteen 2-cubic-foot bags.
Raised bed soil calculatorDoes Niwa work offline, and do I need an account?
The whole plant library and all your layouts are stored on the device, so the app works with no signal — useful on an allotment. There is no account to create and your garden data is never uploaded to a server.
See what's includedWhich growing zones and countries does Niwa support?
Niwa works worldwide. It recognises USDA hardiness zones in the United States and derives frost dates from your location elsewhere, including the UK, Canada, Australia and Europe.
Find your frost dates and zoneHow is Niwa different from other garden planner apps?
Three things: it is a native iPhone app rather than a desktop planner viewed in a mobile browser, it shows companion-planting conflicts on the grid as you place plants instead of in a separate chart, and it works fully offline with no account.
Compare Niwa with other plannersIs Niwa available on Android?
Not yet. Niwa is a native iPhone app and needs iOS 18.0 or later. An Android version is not currently available.
Read the gardening guides in the meantime