Transformer Calculator — Turns Ratio, Voltage & Current CalculatorIdeal Transformer — Step-Up · Step-Down · Power · EfficiencyVp/Vs = Np/Ns = Is/Ip · Step-Up · Step-Down · Power · Efficiency
Use this free Transformer Calculator to instantly compute all key electrical parameters of an ideal transformer using the fundamental transformer equations: Vp / Vs = Np / Ns = Is / Ip (the turns ratio equation) and Vp × Ip = Vs × Is (conservation of power in an ideal transformer) — where Vp and Vs are the primary and secondary voltages (V), Np and Ns are the primary and secondary turns (winding ratio), and Ip and Is are the primary and secondary currents (A). Enter any known values to solve for all remaining transformer parameters: turns ratio (Np : Ns) · secondary output voltage (Vs) · secondary output current (Is) · transformer apparent power (VA or kVA) · step-up or step-down ratio classification.
This online transformer calculator is applied across all areas of electrical engineering and power systems: step-up transformer design — increasing voltage for long-distance power transmission, step-down transformer sizing — reducing mains voltage (230V/110V) for low-voltage electronics, isolation transformer calculations for electrical safety, audio transformer impedance matching in amplifier circuits, switch-mode power supply (SMPS) transformer turns ratio design, and electrical engineering coursework and A-Level / AP Physics exam problems. Understanding the transformer turns ratio is fundamental to Faraday's Law of electromagnetic induction, AC power distribution, voltage regulation, and the entire global electrical grid infrastructure. Trusted by electrical engineers, power systems engineers, electronics designers, electricians, and physics students worldwide.
⚠ Engineering Disclaimer: This transformer calculator assumes an ideal transformer with 100% efficiency — zero winding resistance, zero core losses, and perfect magnetic coupling. Real-world transformers deviate due to: copper losses (I²R winding resistance), core losses (hysteresis and eddy current losses), magnetic flux leakage, magnetizing current and no-load losses, and temperature-dependent resistance changes — resulting in typical real transformer efficiencies of 95–99% for power transformers. For safety-critical power transformer design, grid infrastructure, or high-voltage applications, always consult a licensed electrical engineer following IEC 60076, IEEE C57, and IS 2026 transformer standards.
Primary Side
Secondary Side
Related Electrical & Engineering Calculators
Ohm’s Law Calculator
Calculate voltage, current, or resistance using Ohm’s law.
Electrical Power Calculator
Determine electrical power from voltage and current.
Electrical Resistance Calculator
Compute resistance using electrical formulas and units.
Capacitor Calculator
Calculate capacitance and charge in capacitor circuits.
Energy Calculator
Calculate energy using power, force, or physics formulas.
Scientific Calculator
Perform advanced engineering and mathematical calculations.
Transformer Calculator — Turns Ratio, Voltage, Current, and Impedance Transformation
Transformers transfer electrical energy between circuits through magnetic coupling while transforming voltage and current according to the turns ratio. A transformer with 1,000 primary turns and 100 secondary turns has a 10:1 turns ratio: it steps voltage down by 10 and current up by 10. 240V primary becomes 24V secondary; 1A primary becomes 10A secondary. Power is conserved (minus losses): 240VA in, 240VA out. The transformer calculator computes all secondary quantities from primary inputs and turns ratio, covering step-up, step-down, and isolation configurations.
Impedance transformation is the less obvious but equally important transformer function. An impedance connected to the secondary appears at the primary as that impedance multiplied by the turns ratio squared. A 8Ω speaker connected through a 10:1 step-down transformer appears as 800Ω at the primary — allowing a high-output-impedance tube amplifier to drive a low-impedance speaker efficiently. Audio output transformers, impedance matching networks, and antenna tuners all use this impedance transformation property. The calculator includes the impedance multiplication calculation.
Real transformer efficiency depends on core losses (hysteresis and eddy currents) and copper losses (I²R in windings). Large power transformers achieve 98-99% efficiency; small signal transformers may be 90-95%. Efficiency matters for sizing — a 1 kVA transformer at 95% efficiency dissipates 50W as heat, which must be accommodated in the thermal design. The calculator includes an efficiency factor so the primary VA requirement reflects actual power drawn rather than the ideal theoretical value.