How does the state of California measure prison overcrowding? It looks at the total number of people in its prisons and compares it to the combined capacity of its 35 state prisons - the Supreme Court ordered California to decrease its prison population to 137.5% of the system's designed capacity. Yet 15 out of the state's 35 prisons have populations exceeding 137.5%. Is that the correct way to measure overcrowding? This post explores why an aggregated measure like this can be misleading, and suggests a few simple alternatives.