Transformer Turns Calculator

At a glance:A transformer is a power device that uses electromagnetic induction to convert one AC voltage into another — the core component of modern power systems and many appliances (chargers, power bricks). Its basic structure winds two (or more) coils on a shared iron core: the one connected to the source is the primary (Np turns), the one connected to the load is the secondary (Ns turns). When AC flows in the primary, it creates a changing magnetic flux in the core; as that flux links the secondary, Faraday's law induces a voltage there. For an ideal transformer (no loss, fully coupled flux), the primary-to-secondary voltage ratio equals the turns ratio: Vs/Vp=Ns/Np, so the secondary voltage Vs=Vp×(Ns/Np). Vp is primary voltage (V), Np primary turns, Ns secondary turns. Using the defaults: Vp=220 V, Np=1100, Ns=100 → Vs=220×(100/1100)=20 V, a step-down transformer (fewer secondary turns, lower voltage). If Ns>Np it is a step-up transformer (higher voltage). A transformer only changes AC voltage — exactly why AC became the transmission standard: plants step voltage up very high (reducing long-distance current and heat loss), then step it down to safe use levels at the user end (e.g. Hong Kong 220 V). For an ideal transformer, because power is conserved (input = output, Vp·Ip=Vs·Is), raising voltage lowers current proportionally, and vice versa — the current ratio is inverse to the turns ratio: Is/Ip=Np/Ns. Applications are vast: power transmission/distribution, phone and laptop chargers (220 V→low), doorbell and toy low-voltage supplies, audio and industrial impedance matching, welders (high current, low voltage). Notes: (1) this formula is for an ideal transformer; real ones have copper loss (winding resistance heat) and iron loss (eddy + hysteresis), efficiency typically >95% but not 100%; (2) a transformer only works on AC — DC produces no changing flux and cannot transform; (3) use consistent units for voltage and turns; (4) this calculator takes non-negative values, Np>0. In short, from primary voltage and primary/secondary turns this tool quickly gives secondary voltage and turns ratio, a practical aid for understanding transformer step-up/down and distribution.