Porosity can be measured using sonic and density logs. Sonic logs measure the interval transit time of a sound wave through rock, with denser rock having faster transit times and more porous rock having slower times. There are two methods to calculate porosity from sonic logs: using an equation involving transit time and mud/rock properties, or using a sonic porosity chart. Similarly for density logs, porosity can be calculated from an equation using bulk and grain densities of the formation and mud, or looked up on a density porosity chart. Together, sonic and density logs provide good indications of porosity when used in combination.