We report the angular diameter measurement obtained with the VINCI/VLTI instrument on the nearby star Procyon A ( \alpha CMi A , F5IV-V ) , at a relative precision of \pm 0.9 % .
We obtain a uniform disk angular diameter in the K band of \theta _ { UD } = 5.376 \pm 0.047 mas and a limb darkened value of \theta _ { LD } = 5.448 \pm 0.053 mas .
Together with the hipparcos parallax , this gives a linear diameter of 2.048 \pm 0.025 D _ { \odot } .
We use this result in combination with spectroscopic , photometric and asteroseismic constraints to model this star with the CESAM code .
One set of modeling parameters that reproduces the observations within their error bars are an age of 2 314 Myr , an initial helium mass fraction Y _ { i } = 0.301 and an initial mass ratio of heavy elements to hydrogen ( \frac { Z } { X } ) _ { i } = 0.0314 .
We also computed the adiabatic oscillation spectrum of our model of Procyon A , giving a mean large frequency separation of \overline { \Delta \nu _ { 0 } } \approx 54.7 \mu Hz .
This value is in agreement with the seismic observations by Martić et al. ( [ ] , [ ] ) .
The interferometric diameter and the asteroseismic large frequency spacing together suggest a mass closer to 1.4 M _ { \odot } than to 1.5 M _ { \odot } .
We conclude that Procyon is currently ending its life on the main sequence , as its luminosity class indicates .