So you have a plant leaf and need to measure its surface area. How to do this calculation? There are a couple of methods — starting from old-fashioned and finished with mobile-based apps.
Millimeter graph paper. You need to outline a leaf and calculate squares. This is a very chip and simple method but it requires long hours for measuring leaf area if you have more than one leaf to measure. Also results of measurement are not too accurate.
PC software (ImageJ, Adobe Photoshop, WinFOLIA, etc.). To make leaf area measurement, you need to have a photo or scan of a plant leaf and further processing is based on work with leaf digital image. In most cases this method provides quite precise results but you need to become a guru of using this software. Every application has specific options and conditions in order to measure leaf surface area.Leaf Area Scanners — handhold, portable (LI-Cor, CID, WinDIAS). Good stuff for non-destructive methods of leaf area measurement. You need to take a leaf area scanner with you and go to the field. This equipment provides accurate results and is comfortable to use. But they are too expensive for an ordinary farmer or scientist. Also, they have a problem of saving data: you cannot synchronize your leaf area measurement with data cloud or your PC.
Mobile apps. There are two known Android-based mobile apps to measure leaf area: Petiole and Easy Leaf Area. Both of them are free to download, have an affordable price and provide precise plant leaf data. The way how they work is almost intuitive: open app, calibrate camera, place a leaf in front of a camera and press the button on the screen. The app shows leaf area measurement in square centimeters. However, Petiole goes a little bit further and provides more options for work. If you have more than one leaf area measurement, this app will show you average leaf area and also there is an option to make an experimental comparison of different leaves.
Instead of a conclusion, it would be good to highlight that you can reach your agriculture goal and measure leaf area with any of these methods.