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John's first formula was not quite complete; it missed the x 50/f to calculate the B. 
I think you two Members are confirming that John's first equation is correct.
All that's missing is the one missing assumption for which the stated formula hold true. i.e. 1T. He has already confirmed the 50Hz. 
Am I correct in guessing that the extra 10% for Turns on the secondary is related to a transformer regulation of 10%?
In which case that +10% should be replaced by the target regulation. I can see that turns ratio primary:secondary is an easier way to get to secondary turns. But, knowing the primary T/V is useful for many subsequent design calculations. 
That is right Andrew (your post #12)
The complete formula is: B = 50/f x 45 / (Afe x N) x U, where f = frequency in Hz; U = rms value of voltage in V; Afe = magnetic core crosssection in cm²; B = flux density amplitude in T; N = number of turns. Source: Vacuumschmelze data on GOSS ccores. Please note that for other core configurations the value "45" might be slightly different. 
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Regulation is a more complex function of currents and flux density. Transformers working towards core saturation will be more "regulating" than transformers working at or below 1T. 
Could you express a simple way to use or modify John's second equation.
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Can you see a way to address this? 
Andrew,
When interested I can give the full equations for a calculation, based on a "non regulating" type (I don't like transformers working at their limits). 
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equations are fine, they are mere guides as to how to proceed with traffo buildup....design is iterative process.... what happens if you find out that winding primary you end up with 5.5 layers? you can either use a bigger wire if space permits, use a smaller wire, make it 6 full layers and adjust the turns, or use smaller number of turns with just 5 layers.............or you can wind a screen winding....... there are many design choices one can make, as long as you stay below the knee of the magnetization curves, you are able to do any of these things.... bottomline, whatever figure that comes out of the formula does not mean you have to stick to it, it never happens that way in the real world..... 
Thanks to all reply,
now I can recalculate every things, every thinks too :):) my formula is OVERSIMPLIFIED, yes because I like simple things but works nice So that is the complete formula. I just remember the 45 * V/A but don't know where its come from for the 49.5, I get from 45 * 10%, just for minimize the looses from the cooper wire so its for regulation too Then for the wire to be used to winding from the book that I was read about 9 years ago (don't have any note just from memories in my head) get this Allowable currents to flow in the cooper wire per area (cm²) symbol S S = 3A to 5A per cm² for 100VA transformer I use 0.25 to 0.3mm diameter cooper wire for primariy (220volt) for secondary I use as thick as possible from winding window left Is this formula okay or not? Thanks 
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