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Free garden planning calculators
Four tools that answer the arithmetic questions every gardener hits in spring. No sign-up, nothing to install, and they work on your phone. Use them freely — and link to them if they help someone.
Plants per square foot calculator
Pick a crop and bed size, get the per-square count and the total. Includes a full spacing chart for 60+ vegetables, herbs and fruit.
Raised bed soil calculator
Cubic feet, cubic yards, litres and bags for any bed size, in metric or imperial — plus the Mel's Mix three-way split.
Plant spacing calculator
Turn any spacing into a real plant count, and compare square grid against offset triangular spacing — worth about 15% more plants.
Frost date & sowing schedule
Enter your last frost date and get sow-indoors, plant-out and autumn deadline dates for 22 crops, plus your season length.
Which one do you need?
| Your question | Tool |
|---|---|
| “How many carrots fit in a square?” | Plants per square foot |
| “How many bags of compost do I buy?” | Raised bed soil |
| “The packet says 20 cm — how many is that?” | Plant spacing |
| “When do I start tomatoes indoors?” | Frost dates |
| “Can I still sow beetroot in August?” | Frost dates |
| “Is my bed deep enough for parsnips?” | Raised bed soil |
The order to use them in
Size and fill the bed
Decide dimensions and depth, then work out volume and what to buy. Soil calculator →
Decide what goes in each square
Assign crops square by square and check the counts. Plants per square →
Handle any non-standard spacings
For crops whose packet spacing doesn't fit the neat 3/4/6/12-inch pattern. Spacing calculator →
Put dates against everything
Work out what to sow when, and buy seed from that list. Frost dates →
Using these on a site or in a class? Go ahead — they're free to use and free to link to. If they saved you an afternoon, a link back is the only thanks we ask for.
Guides that go deeper
- Square foot gardening — the full method, spacing chart and layouts
- How to plan a vegetable garden — before you build anything
- When to start seeds indoors
- Companion planting guide
These four tools live inside the app too.
Niwa runs all of this automatically across every bed you plan. Free on iPhone.
Questions gardeners ask
Is 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