Context : The knowledge of mass loss rates due to thermal winds in cool dwarfs is of crucial importance for modeling evolution of physical parameters of main sequence single and binary stars .
Very few , sometimes contradictory , measurements of such mass loss rates exist up to now .

Aims : We present a new , independent method of measuring an amount of mass lost by a star during its past life .

Methods : It is based on the comparison of the present mass distribution of solar type stars in an open cluster with the calculated distribution under an assumption that stars with masses lower than M _ { \mathrm { lim } } have lost an amount of mass equal to \Delta M .
The actual value of \Delta M or its upper limit is found from the best fit .

Results : Analysis of four clusters : Pleiades , NGC 6996 , Hyades and Praesepe gave upper limits for \Delta M in three of them and the inconclusive result for Pleiades .
The most restrictive limit was obtained for Praesepe indicating that the average mass loss rate of cool dwarfs in this cluster was lower than 6 \times 10 ^ { -11 } M _ { \sun } /yr .
With more accurate mass determinations of the solar type members of selected open clusters , including those of spectral type K , the method will provide more stringent limits for mass loss of cool dwarfs .

Conclusions :