Passive margins form by rifting and extension of continental crust. Extension of continental crust, associated with subduction elsewhere, decreases ocean basin volume, forcing sea level to rise. The amount that the continental crust has been extended can be quantified using total tectonic subsidence, which is determined using sediment thickness and water depth data coupled with a model of the rifting process. We calculate total tectonic subsidence, the amount of extension or stretching factor, and thickness of extended continental crust at a 5 min grid resolution for passive margins between 77 degrees N and 70 degrees S. Our modeled crustal thicknesses correlate well with seismic refraction data from North America and Australia and can be used to estimate the change in ocean volume and the impact of extension on sea level. The duration of extension is constrained by estimating the onset of rifting and the breakup age, which is the time when rifting ceased and seafloor spreading began. Our results indicate that extension of continental crust has increased sea level by 20.8 m since the start of Pangea rifting.