The total porosity of a container medium is often inaccurate when determined from a water release curve because the use of the total porosity value and bulk density in the equation, Total porosity = (1 ‐ bulk density/particle density) x 100, gives an unrealistic value for particle density. The inaccuracy seems to be caused by incomplete saturation of the medium sample at zero suction. Total porosity should be calculated using bulk density and particle density, rather than equating total porosity with the zero suction value on the water release curve. The zero suction value is a measure of effective porosity since it does not take into account trapped air in the medium.