I know it's possible to calculate VA ratings from cross section of the core in cm. I used to do that when I was young, but forgot it .....

so is it posible to measure VA from the dimensions? if yes pls remeber how you did

It is, but you have to know what to measure... Dimensions of the core are selected in the way that they don't have too much magnetic flow (is flux the propper english word? not sure here).

When you are calculating the transformer, you calculate the input power first. Then select the magnetic flux density (

*B*) you want to have (usually B=1T - tesla). The area of the cross section of core should be

*S*=sqrt(

*P*/

*B*), with that 1T it's just S=sqrt(P).

I made a quick image so you'd know what I mean by area of the cross section of core. It's

**S = l*d**, just the middle grey area (dimensions of whole transformer as you posted won't help that much).

So power that you want to get

**from the output **should be about 85% of input, because you are just calculating it, i would go with 70%...

P

_{o}=70%*S

^{2}=0,7*(l*d)

^{2}