What is Theoretical and Practical Coverage of paint?

 The theoretical coverage rates quoted on the manufacturer’s data sheets all conform to a pure mathematical formula. 

In most cases, wastage is caused by some paint being left in the tin, paint left on the roller and in the tray, and over-spraying past the object you are painting. As a general rule, contractors allow for a 10-30% wastage for most coatings. Coverage after consider %wastage we called Practical Coverage.  

The  theoretical coverage(TC) rate have to calculate bellow formula

Volume solids x 10
DFT

The volume solids must  be calculated after thinning, suppose Product TDS has Vs-50, So, after 10% thinning Vs will be (50/100+10)*100 = 45.45. 

For example, if Vs after thinning is 45.45, DFT =60, 

TC= 45.45*10/60 =7.57 m2/Ltr

If loss factor is 30%

PC={TC-(TC*%loss)/100}

    ={7.57-(7.57*30/100}

    = 5.299 m2/Ltr

Thanks for your attention