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For grow lights and window light

DLI Calculator for Indoor Plants

Find out whether your plant gets enough light in a day, and how many hours to run your grow light.

No special tools or know-how needed. Pick your plant, tell us about its light, and get a plain answer.

New to plant light? Start hereA 1-minute read

Most plant owners have never heard these words, and you don’t need to know them to use this calculator. Here they are in plain words:

DLI
Your plant’s “daily dose” of light: all the light it gets in one day. This is what the calculator works out.
PPFD
How strong a grow light is at the leaves. Grow light makers print it on a chart.
Lux
How bright a spot is, as a phone app or light meter measures it.
Footcandles
An older US unit for the same brightness (1 footcandle is about 11 lux).

Which option is for me?

Want the longer version? What is DLI, explained simply.

1Pick your plant

Pothos, spider plant, dracaena, rubber plant, fiddle-leaf fig, prayer plant, peperomia

2Check the light

Not sure? Choose “Describe the window”: no tools needed.

Where do I find this number?

Most grow lights come with a PPFD chart (sometimes called a PAR map). Look on the box, in the manual, or in the photos of the online listing. It shows how strong the light is at different heights below the lamp.

Example only: “PPFD at 18 in” 180 240 180 240 320 240 180 240 180 Use the middle number for the height you hang it
  1. Find the chart for the height your light hangs above the leaves (for example 12, 18 or 24 inches).
  2. Use the number in the middle, right under the lamp. In this example, 320.
  3. No chart in the box? Search the light’s brand and model name plus “PPFD”.

Only see watts? Watts measure electricity, not plant light, so they can’t be used here. Measure the light with your phone instead.

3Hours of light a day

Your plant’s daily light

Enter your light reading to see your plant’s daily light.

Example: a grow light giving 200 µmol/m²/s for 12 hours gives a daily light (DLI) of 8.6, about right for pothos or a spider plant.

How do you calculate DLI?

Multiply the light intensity at the leaves (PPFD) by the hours the light is on each day, then by 0.0036:

DLI = PPFD × hours × 0.0036

The 0.0036 turns seconds into hours (× 3,600) and micromoles into moles (÷ 1,000,000). For example, 200 µmol/m²/s for 12 hours gives 200 × 12 × 0.0036 = 8.6 mol/m²/day.

Read the full explanation of DLI

How do I convert PPFD to DLI?

Use the same formula. PPFD is light per second, and DLI adds it up over the whole day. A quick shortcut: at 12 hours of light, DLI is PPFD × 0.0432; at 16 hours, PPFD × 0.0576.

Use the PPFD to DLI converter

What should my DLI be?

It depends on the plant. University extension guidance gives these daily ranges in mol/m²/day:

  • Low-light houseplants: 3–6
  • Medium-light houseplants: 6–10
  • African violets and moth orchids: 6–10
  • Microgreens: 9–12
  • Vegetable and flower seedlings: 10–12
  • Succulents and cacti: 12–16
  • Herbs and leafy greens: 12–17
  • Tomatoes, peppers and other fruiting plants: 18–30

See the full DLI chart by plant, with sources

How do you calculate DLI for plants without a PAR meter?

Measure lux with a light meter or a free phone app, convert lux to PPFD (for sunlight, divide by 54), then use the formula above. Phone readings are rough but good enough to compare spots.

Use the lux to DLI converter

How much PPFD do I need for a target DLI?

Turn the formula around: PPFD = DLI ÷ (hours × 0.0036). Basil wanting 12 mol/m²/day under 14 hours of light needs about 238 µmol/m²/s.

Use the DLI to PPFD converter

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