DLI Calculator (Daily Light Integral)

DLI equals PPFD times the photoperiod converted to seconds, divided by one million. In formula form: DLI = PPFD x hours x 3600 / 1,000,000, which gives mol per square meter per day.

As a rough guide, under about 12 suits leafy greens and low-light houseplants, 12 to 30 covers most fruiting and flowering crops, and above 30 favors sun-loving crops. Species targets vary, so treat the bands as starting points.

Measure PPFD with a quantum or PAR meter held at canopy height, or read the manufacturer PPFD map for your fixture at its hanging height. Averaging several points across the canopy gives a fairer number.

No. It uses one average PPFD for the whole photoperiod, so a real canopy with bright centers and dim edges is not captured. Sample several spots and average them before entering a value.

A day has only 24 possible hours of light, so the tool rejects anything above 24. Many crops also need darkness for respiration and flowering, so a longer day is not automatically better.

Yes, DLI scales directly with hours. Doubling the photoperiod at the same PPFD doubles the DLI, which is why a modest PPFD over a long day can match an intense light over a short one.

PPFD is entered in micromoles per square meter per second (umol/m2/s) and the result is in moles per square meter per day (mol/m2/day). The 3600 and one-million factors handle the seconds and the umol-to-mol conversion.

No. The DLI is computed in your browser with JavaScript, so nothing you enter leaves your device. You can keep using the page offline after it loads.

Pair this with the grow light coverage calculator to check the footprint your fixture lights, and with the EC to PPM and hydroponic nutrient calculators to match feeding to your light level.