Transformer Ratio Calculator
Enter primary/secondary turns (Np, Ns), primary voltage and current to compute turns ratio n=Np/Ns, voltage ratio, current ratio, Vs and Is. Np=1000, Ns=100, Vp=100, Ip=1 → Vs=10 V, Is=10 A (step-down).
Input Data
Results
At a glance:Transformer turns ratio (Transformer turns ratio, 1831): an ideal transformer has Np primary turns and Ns secondary turns; by Faraday's electromagnetic induction the same changing flux Φ induces Vp=Np·dΦ/dt and Vs=Ns·dΦ/dt in the two coils, so Vp/Vs=Np/Ns. Energy conservation Pp=Ps, i.e. Vp·Ip=Vs·Is, gives Ip/Is=Ns/Np=Vs/Vp. Define the turns ratio n=Np/Ns: (1) n>1 step-down (Vs<Vp, Is>Ip), e.g. power 11 kV→220 V; (2) n<1 step-up (Vs>Vp, Is<Ip), e.g. 220 V→11 kV; (3) n=1 isolation (same voltage and current, only circuit isolation). Ideal transformer assumes: no flux leakage, no winding resistance, no core loss; real efficiency 95–99%. Classic examples: (1) phone charger Np:Ns=22:1, 220 V→10 V; (2) power step-down Np:Ns=50:1, 11 kV→220 V; (3) microwave HV Np:Ns=1:8, 220 V→2000 V; (4) current transformer Np:Ns=1:100, 100 A→1 A measurement. History: Faraday discovered mutual induction in 1831; Henry independently; Gaulard and Gibbs invented the commercial transformer in 1885. Applications: (1) power step-up/down — transmission and distribution; (2) isolation transformers — medical, marine; (3) current transformers — measuring large currents; (4) impedance matching — RF circuits; (5) ignition coils — car engines.
Formula
Turns ratio: n = Np / Ns
Voltage ratio: Vp / Vs = Np / Ns = n
Current ratio: Ip / Is = Ns / Np = 1/n
Secondary voltage: Vs = Vp · (Ns / Np) = Vp / n
Secondary current: Is = Ip · (Np / Ns) = Ip · n
$$\frac{V_p}{V_s} = \frac{N_p}{N_s} = \frac{I_s}{I_p}, \quad V_s = V_p \cdot \frac{N_s}{N_p}, \quad I_s = I_p \cdot \frac{N_p}{N_s}$$How to Use
- Enter primary turns Np and secondary turns Ns.
- Enter primary voltage Vp and current Ip.
- The tool gives turns ratio n=Np/Ns, voltage ratio, current ratio, Vs and Is.
Case Studies
Power transmission and current transformers
Power step-down Np:Ns=50:1, 11 kV→220 V; current inversely, so a 220 V/11 kV transformer carries 50× more current on the low side.
Current transformer Np:Ns=1:100, 100 A→1 A for the meter — isolates and scales large currents safely.
Phone charger Np:Ns=22:1, 220 V→10 V, with a bridge rectifier to DC.
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.