| | San Ramon, CA | Rancho Santa Margarita, CA | United States |
| Population | 85,688 | 48,190 | 329,725,481 |
| Female Population | 50.0% | 51.0% | 50.5% |
| Male Population | 50.0% | 49.0% | 49.5% |
| Median Age | 40.6 | 39.7 | 38.4 |
| space3 | | | |
| Population - 2010 | 71,784 | 47,877 | 309,327,143 |
| Population - 2000 | 44,722 | 47,214 | 285,036,114 |
| Population - 1990 | 35,303 | 11,390 | 251,960,433 |
| Pop. 2000 to Now | 85.3% | 0.8% | 15.6% |
| Pop. 1990 to Now | 134.7% | 317.6% | 30.8% |
| space4 | | | |
| Population Density | 4,585.4 | 3,738.0 | 93.4 |
| Land Area | 18.7 | 12.9 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | San Ramon, CA | Rancho Santa Margarita, CA | United States |
| Age 0 to 4 | 5.2% | 6.4% | 5.9% |
| Age 5 to 9 | 7.6% | 5.8% | 6.1% |
| Age 10 to 14 | 9.8% | 7.1% | 6.6% |
| Age 15 to 17 | 5.5% | 4.2% | 3.9% |
| Age 18 to 20 | 3.0% | 3.6% | 4.0% |
| Age 21 to 24 | 3.4% | 3.9% | 5.2% |
| Age 25 to 34 | 8.2% | 11.8% | 13.8% |
| Age 35 to 44 | 15.9% | 15.0% | 12.9% |
| Age 45 to 54 | 18.6% | 16.1% | 12.6% |
| Age 55 to 59 | 7.0% | 8.8% | 6.7% |
| Age 60 to 64 | 4.7% | 7.3% | 6.3% |
| Age 65 to 74 | 6.5% | 6.0% | 9.6% |
| Age 75 to 84 | 3.4% | 2.5% | 4.5% |
| Age 85 and over | 1.2% | 1.5% | 1.9% |
| space1 | | | |
| Race | | | |
| | San Ramon, CA | Rancho Santa Margarita, CA | United States |
| White | 35.9% | 60.5% | 59.4% |
| Black | 2.8% | 1.9% | 12.2% |
| Asian | 47.6% | 11.1% | 5.6% |
| Native American | 0.1% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.5% | 0.0% | 0.2% |
| Other | 0.2% | 0.2% | 0.4% |
| Two or More Races | 5.0% | 5.5% | 3.2% |
| Hispanic | 7.9% | 20.6% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | San Ramon, CA | Rancho Santa Margarita, CA | United States |
| Married Population | 63.9% | 59.4% | 49.8% |
| Currently Married | 63.0% | 58.6% | 48.0% |
| Married but Separated | 0.9% | 0.8% | 1.8% |
| Single Population | 36.1% | 40.6% | 50.2% |
| Never Married | 25.4% | 28.2% | 33.8% |
| Divorced | 7.4% | 9.5% | 10.8% |
| Widowed | 3.3% | 2.9% | 5.6% |
| space5 | | | |
| Household Size | 2.94 | 2.86 | 2.60 |
| Households | 29,084 | 16,825 | 124,010,992 |
| Family Households | 22,947 | 13,008 | 80,755,759 |
| Married couple, w/children | 53.1% | 41.8% | 30.5% |
| Married couple, no children | 32.5% | 41.3% | 42.9% |
| Non Family Households | 6,137 | 3,817 | 43,255,233 |
| Single householder, w/children | 8.6% | 6.9% | 15.8% |
| Single householder, no children | 5.7% | 10.0% | 10.8% |