Online acidity charts are available through the websites of Washington University, Greenopedia, the Gardenhelper.com and Coffeeresearch.org. Charts on these websites compare the relative acidity of a variety of substances, such as food and soils.
Washington University provides a chart outlining the strength of acid and base compounds. Greenopedia provides a chart of the relative acidity of a variety of foods, including lobster, farina and chard. The chart rates foods on a scale from "very low" to "highly" acidic.
Gardenhelper.com provides an acidity chart to aid gardeners in choosing the proper fruits and vegetables to grow in soils with different pH levels. A highly detailed chart of the acidic components of coffee is available at Coffeeresearch.org.