Calculating Irregular Leaf Area for the LI-6400XT

The LI-6400XT Portable Photosynthesis System calculates photosynthetic rates, transpiration, and other variables based on the leaf area inside the chamber. The standard leaf chamber has an aperture of 2 cm x 3 cm, so if the sample leaf covers the entire aperture, then the leaf area is 6 cm2.

But what if the leaf doesn’t cover the entire chamber opening?  In this case, the user will need to measure or estimate the leaf area so that the calculations are correct.

Here is a simple method to measure the area of the leaf inside the chamber during a measurement.  It does require removing the leaf from the plant (destructive sampling), but it provides a more accurate value than a cursory approximation.

1.  Perform the photosynthesis measurement.  Don’t forget to match the IRGAs before you start—matching is especially important for plants with small leaf areas.

2.  Before removing the leaf from the chamber, trace the outline of the bottom gasket on the leaf surface with a pen.

3.  Open the chamber and remove the leaf.

4.  Remove the leaf from the plant.

5.  Find a spare gasket.

6.  Line up the outside edge of the gasket over the pen marks.

7.  Trace the inside of the gasket on the leaf surface with the pen.

8.  Cut out the area traced by the inner pen mark.  This was the portion of the leaf that was inside the chamber during the measurements.

9.  Measure the area of this section.  You can easily use the LI-3100C Area Meter or the LI-3000C Portable Area Meter with the LI-3050C Transparent Belt Conveyor Accessory to measure this leaf area.  You can also scan the section, or take a photograph of it resting on a white table or piece of paper, next to a ruler or measuring tape.  Then use image-processing software, such as ImageJ, to analyze the pixels and calculate area.  An alternative method, though less precise, is to trace the leaf onto graphing paper and estimate the area.

10.  Recompute the data using the correct leaf area.  This is further described in Chapter 13 of the LI-6400XT manual.

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This article was originally posted on Thursday, August 16th, 2012.

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4 Responses to “Calculating Irregular Leaf Area for the LI-6400XT”

  1. Frank says:

    May I please request for more information on how to measure photosynthesis on mimosa family species such as Black locust (Robinia pseudoacacia)?
    Is there a special leaf chamber for mimosa family?


  2. LI-COR –Abby Schipporeit says:

    Hello Frank!

    Thanks for your comment. R. pseudoacacia does have fairly dissected leaflets, but they’re usually large enough that they can fit into the standard 2×3 chamber without too much trouble. Try to put one leaflet at a time into the chamber. If you need to use two small leaflets, make sure there’s no overlap between them.

    If you have any questions about this, please feel free to contact our tech support team.

  3. Munawar khan says:

    how we calculate maize leaf area send formula

  4. LI-COR –Abby Schipporeit says:

    Hello Munawar!

    Thank you for your comment. Generally, maize leaves are large enough not to require much leaf area recalculation. However, if you are working with a smaller leaf or a leaf that has been damaged, the procedure for calculating irregular maize leaf area is the same as any other leaf area. There is no specific formula for this species. If you have any other questions, please feel free to contact our technical support department at