Grow Light Coverage Calculator

It divides the light wattage by a watts-per-square-foot target. The stage defaults are rough LED draw figures: 15 for seedlings, 25 for vegetative growth and 35 for flowering. So 600 watts at the 35 flowering target gives about 17.143 square feet.

Each stage sets a different intensity target because plants need more light as they mature. Seedlings use 15 watts per square foot, vegetative growth uses 25, and flowering uses 35. A higher target divides the same wattage into a smaller covered area.

Use it whenever your fixture, crop or technology does not match the LED stage defaults. Type any watts-per-square-foot value and it replaces the stage number. A 300 watt light at an override of 20 covers 15 square feet regardless of the stage selected.

Use the actual power draw at the wall, not an inflated equivalent rating. Many LED fixtures are marketed with a much higher number than they really consume, which would overstate the coverage the tool reports.

The square foot coverage is multiplied by 0.092903, the number of square meters in one square foot. So 12.8 square feet becomes about 1.189 square meters. Results are rounded to three decimal places.

It is only a rough guideline. LED efficiency, mounting height, reflectivity and beam spread all change real output, so two lights of equal wattage can usefully light very different areas.

Measuring PPFD with a quantum meter and targeting a daily light integral (DLI) is far more precise than any wattage rule. Use this calculator for quick planning, then verify the real intensity at canopy height with light readings.

The stage defaults assume LED draw. For HID or fluorescent fixtures the watts-per-square-foot relationship differs, so enter your own target in the override field to match that technology.

No. The calculation happens entirely in your browser. Your wattage and target values are never sent to a server, logged or stored.