Microgreen Seed Density Calculator: Seed per Tray, Seeds per Square Inch

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Opens on the book's Microgreen Shelf. Change any number to your own and press Calculate.

Start from fills the boxes below

Tray floor, length in, inside

Tray floor, width in, inside

Seed a tray g

Greens a tray g, weighed

Thousand-seed weight g per 1,000 seeds, optional

Scale it to another container (seed covers a floor: scale by area)

Container length in

Container width in

Mix, water and the month

Mix depth in

Mix you plan a tray L

Starting water L of water per L of mix

Trays of this crop in the month

All trays in the month

Enter the tray, the seed and the harvest, then press Calculate.

The formula

Tray floor = length × width (in²; × 6.4516 for cm²)
Seed for any container = seed a tray × its floor ÷ the tray's floor
Greens per gram of seed = greens a tray ÷ seed a tray
Seeds a tray = seed grams ÷ thousand-seed weight × 1,000; per in² = seeds ÷ floor
Mix = floor × depth × 16.387 mL (1 in³); starting water = mix × water ratio
Seed for the month = trays of the crop × seed a tray; mix = all trays × mix a tray

The book's worked example, Chapter 2. Radish: 28 g on a 190.6 in² floor (1,230 cm²), cut at 280 g: 10 g of greens per gram of seed (broccoli 23.1, sunflower 4.7, pea 1.5). At 8.13 g per 1,000 seeds that is 3,444 seeds, about 18 per in². A 5 × 5 in container takes 3.67 g. Mix: 3.12 L, planned as 3 L, so 60 L for the first 20 trays, and about 0.75 L of water to start.

Check it. Weigh 1 g of your seed and count it: 1,000 ÷ your count is your thousand-seed weight. Seed lots differ, so count each new bag.

Honest limits. Seed rates are sellers' and extension planning figures; a seed lot's size and germination change them. The starting water is one extension guide's ratio, not a rule: weigh the watered tray and water back to that weight. The Microgreen Shelf was worked out on paper from published figures, not grown by us: weigh and measure your own. Prices are illustrative US prices from October 2026, shown without a currency sign; put in your own. Everything stays in your browser: no sign-up, nothing stored.

These calculators go with Grow by Numbers (Make It Add Up, Book 1), where every number on this page is worked by hand.