Grow Light Calculator

Grow light sizing depends on growing area, plant type, and light technology. The key metric is PPFD (Photosynthetic Photon Flux Density) measured in μmol/m²/s.

Required Watts = Growing Area × Watts per sq ft (or sq m)

Required Lumens = Growing Area × Lumens per sq ft (or sq m)

Unit conversions:

• 1 sq ft = 0.0929 sq m
• 1 sq m = 10.764 sq ft
• 1 foot = 0.3048 meters
• 1 meter = 3.281 feet

Watts per square foot by plant type (LED):

• Leafy greens/herbs: 20–30 W/sq ft (215–323 W/sq m)
• Vegetables (vegetative): 30–40 W/sq ft (323–430 W/sq m)
• Flowering/fruiting plants: 40–60 W/sq ft (430–645 W/sq m)
• Seedlings/clones: 15–20 W/sq ft (161–215 W/sq m)

PPFD targets by growth stage:

• Seedlings/clones: 100–300 μmol/m²/s
• Vegetative growth: 300–600 μmol/m²/s
• Flowering/fruiting: 600–1,000 μmol/m²/s

Hanging height guidelines (LED):

• Seedlings: 24–36 inches (60–90 cm)
• Vegetative: 18–24 inches (45–60 cm)
• Flowering: 12–18 inches (30–45 cm)

Note: LED is ~2x more efficient than HPS/HID. If using older technology, double the wattage recommendations.