Photosynthetic Rate Calculator

What it does

This estimates how fast a leaf is making sugar (photosynthesis) under a given amount of light, CO₂, and temperature. PPFD is the amount of usable grow light hitting the leaf (micro-moles of photons per square metre per second); VPD is how thirsty the air is. It uses a standard textbook light-response curve (a non-rectangular hyperbola) — plants speed up with more light but eventually plateau.

When to use it

When you are deciding how hard to push light and CO₂ and want to see roughly where you stop getting a return. It is a single-leaf physiological model, crop-agnostic and best treated as a teaching/what-if tool — real canopy performance depends on leaf area and light penetration this does not model. Good for questions like "is it worth adding CO₂?" or "am I already past the light saturation point?"

What you enter

PPFD(µmol/m²/s)

CO₂ Concentration(ppm)

Leaf Temperature(°C)

VPD(kPa)

What you get

Net Photosynthesis(µmol CO₂/m²/s)

Transpiration Rate(mmol H₂O/m²/s)

Water Use Efficiency(µmol/mmol)

Light Sat. Point(µmol/m²/s)

Reading the result

Net Photosynthesis is the useful output — higher is better, but watch how it flattens as you raise PPFD past the Light Saturation Point; light added beyond that point is largely wasted energy. Raising CO₂ lifts the whole curve, and the temperature term peaks near 28 °C and falls off either side. Water Use Efficiency (photosynthesis per unit of water transpired) drops as VPD climbs, so a very high WUE at low VPD with strong photosynthesis is the sweet spot. These are per-leaf estimates from generic coefficients — use them to compare scenarios, not to predict exact yield.

Related calculators

• Weather-Adaptive Controls
• Chlorophyll Fluorescence
• Crop Planner
• Disease Risk Index