Converting your plot based data to “per m²"

Earthworm data is generally reported on a per square meter basis (#/m²). If you use a plot size of 33cm x33cm, then simply multiply the plot data (number, biomass or species of earthworms per plot) by 9 to get the same data “per m²”. This is simply the result of the fact that your sample plot is 1/3rd of a meter of each side (~33 cm) or 1/9th of a m² (see illustration below).

Calculating earthworm density (number/m²)

Using density (the number of earthworms) as an example, if you collected 13 earthworms from your ~33cm x 33cm sample area, then the density of earthworms per m² is 9 x 13 = 117/m²