Enter values to see results
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g/cm²/h
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mmol/m²/s
Enter values to see results
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g/cm²/h
—
mmol/m²/s
The Transpiration Rate Calculator determines the rate of water loss from plant leaves based on gravimetric measurements. Transpiration is the process by which water evaporates from leaf surfaces, primarily through stomata. It is a critical component of the water cycle and drives the upward movement of water and nutrients through the xylem. Measuring transpiration rate helps researchers understand plant water relations, stress responses, and ecosystem water budgets.
This calculator takes the mass of water lost, the leaf area, and the measurement time to compute transpiration rate in both gravimetric (g/cm²/h) and molar (mmol/m²/s) units commonly used in plant physiology literature.
The calculator uses the gravimetric transpiration formula:
E = Mass Loss (g) / (Leaf Area (cm²) x Time (h))
This gives the rate in g/cm²/h. The conversion to mmol/m²/s is:
E (mmol/m²/s) = E (g/cm²/h) x 10,000 cm²/m² / 18.015 g/mol / 3,600 s/h x 1,000 mmol/mol
In practice, water loss is measured by weighing a potted plant or cut shoot before and after a timed period, or by using a porometer that directly measures water vapor flux from the leaf surface.
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Results
A plant losing 2.5 g of water over 50 cm² of leaf area in 1 hour transpires at 0.05 g/cm²/h or about 7.7 mmol/m²/s.
Inputs
Results
A shaded plant losing only 0.3 g over 100 cm² in 2 hours has a low transpiration rate of 0.23 mmol/m²/s.
Transpiration is influenced by environmental factors (light intensity, temperature, humidity, wind speed) and plant factors (stomatal density, stomatal aperture, leaf area, cuticle thickness). High light, high temperature, low humidity, and wind increase transpiration, while drought stress causes stomatal closure that reduces it.
The gravimetric unit (g/cm²/h) is intuitive and easy to measure with a balance. The molar unit (mmol/m²/s) is preferred in scientific literature because it relates directly to stomatal conductance and can be compared with photosynthesis rates (µmol CO₂/m²/s). This calculator provides both so you can use whichever your context requires.
Common methods include: (1) Gravimetric: weigh a potted plant over time, (2) Potometers: measure water uptake by a cut shoot, (3) Porometers and gas exchange systems: measure water vapor flux directly from leaf surfaces, (4) Sap flow sensors: measure xylem water transport in intact trees. Each method has trade-offs between accuracy, scale, and practicality.
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