With the aim of computing a complete energy balance of front crawl, the energy cost per unit distance (C= Ėv^{−1}, where Ė is the metabolic power and v is the speed) and the overall efficiency (η_{o}=W_{tot}/C, where W_{tot} is the mechanical work per unit distance) were calculated for subjects swimming with and without fins. In aquatic locomotion W_{tot} is given by the sum of: (1) W_{int}, the internal work, which was calculated from video analysis, (2) W_{d}, the work to overcome hydrodynamic resistance, which was calculated from measures of active drag, and (3) W_{k}, calculated from measures of Froude efficiency (η_{F}). In turn, η_{F}=W_{d}/(W_{d}+W_{k}) and was calculated by modelling the arm movement as that of a paddle wheel. When swimming at speeds from 1.0 to 1.4 m s^{−1}, η_{F} is about 0.5, power to overcome water resistance (active body drag × v) and power to give water kinetic energy increase from 50 to 100 W, and internal mechanical power from 10 to 30 W. In the same range of speeds Ė increases from 600 to 1,200 W and C from 600 to 800 J m^{−1}. The use of fins decreases total mechanical power and C by the same amount (10–15%) so that η_{o} (overall efficiency) is the same when swimming with or without fins [0.20 (0.03)]. The values of η_{o} are higher than previously reported for the front crawl, essentially because of the larger values of W_{tot} calculated in this study. This is so because the contribution of W_{int} to W_{tot }was taken into account, and because η_{F} was computed by also taking into account the contribution of the legs to forward propulsion.