Sizu Riatto
Grow by Numbers · Chapter 10

Cost per Tray

A tray costs its seed, its mix and its share of the light. Add what it sells for and the packing, and you have the contribution, and the number that matters most on a full shelf: contribution per shelf-day.

Home › Calculators › Cost per Tray

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

Growing a tray

What the tray brings back (optional)

Enter the seed, the mix and the light, then press Calculate.

The formula

  • Seed = grams ÷ 1,000 × price a kg
  • Mix = liters × (bag price ÷ (quarts × 0.9464 L))
  • Light = watts × lights × hours ÷ 1,000 ÷ trays × days × price a kWh
  • Cost to grow = seed + mix + light
  • Packs = harvest ÷ pack grams; contribution = packs × (price − packing) − cost to grow; per shelf-day = ÷ days
The book's worked example, Chapter 10. Radish: seed 28 g × 23.50 a kg = 0.66; mix 3 L at 0.70 a L = 2.11; light 0.32 kWh × 9 days × 0.18 = 0.52: 3.29 to grow a tray (broccoli 3.20, sunflower 3.63, pea 4.04). Sold in 2 oz packs at 5, it contributes 19.77, 2.20 a shelf-day; sunflower earns most a shelf-day, 2.93.
Check it. The mix costs more than the seed for every one of the four shelf crops: if your seed line is the biggest, check the seed's price per kg.

Honest limits. Seed and mix prices are illustrative and change by supplier and pack size; a 5 lb bag is cheaper per kg than an ounce packet. Harvests are planning figures: weigh yours. Water, your time and the kit are not in the cost to grow. 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.