Context :

Aims : The appearance of two recent supernovae , SN 2011dh and 2005cs , both in M51 , provides an opportunity to derive an improved distance to their host galaxy by combining the observations of both SNe .

Methods : We apply the Expanding Photosphere Method to get the distance to M51 by fitting the data of these two SNe simultaneously .
In order to correct for the effect of flux dilution , we use correction factors ( \zeta ) appropriate for standard type II-P SNe atmospheres for 2005cs , but find \zeta \sim 1 for the type IIb SN 2011dh , which may be due to the reduced H-content of its ejecta .

Results : The EPM analysis resulted in D _ { \mathrm { M 51 } } = 8.4 \pm~ { } 0.7 Mpc .
Based on this improved distance , we also re-analyze the HST observations of the proposed progenitor of SN 2011dh .
We confirm that the object detected on the pre-explosion HST -images is unlikely to be a compact stellar cluster .
In addition , its derived radius ( \sim 277 R _ { \odot } ) is too large for being the real ( exploded ) progenitor of SN 2011dh .

Conclusions : The supernova-based distance , D = 8.4 Mpc , is in good agreement with other recent distance estimates to M51 .