Hand-calculated, with a mix of 25% city, 75% highway driving for both vehicles in practically ideal weather conditions (SF Bay Area).
2015 Civic (R18, 25,000 miles): 39.0 mpg
2008 CR-V AWD (K24, 109,000 miles): 27.9 mpg
A/C on auto and speed with prevailing traffic flow in both cases.