# Calculating the primary to secondary turns ratio of a transformer

Is it possible to determine the turns ratio of a step-down transformer with just the following information?

120V (rms) 50 Hz AC mains supply connected to the primary windings. And a secondary voltage of 10V (rms) at the secondary windings output.

Is it a case of simply dividing both rms voltages given by the formula, Vp/Vs = Np/Ns, or do they need to be converted into their peak value?

## 1 Answer

The rms value is proportional to the peak value so the ration of $V_p/V_s$ will be the same regardless of if you use two peak values or two rms values.

• thanks, just noticed that. so, would that calculation in the turns ration or does the formula need manipulating? – libraryjoe Oct 21 '16 at 19:58
• The ratio of the voltages is the ratio of the number of turns. – M. Enns Oct 21 '16 at 20:01