Transformer Turns Ratio Calculator

This tool calculates the turns ratio (N_p/N_s), secondary voltage (V_s), primary and secondary currents (I_p, I_s), and voltage transformation type (step-up, step-down, or isolation). It uses ideal transformer assumptions—no losses, perfect coupling, and linear magnetic behavior—to derive all values from four user inputs.

Engineers use it during early-stage power supply design, impedance matching for audio or RF circuits, selecting off-the-shelf transformers, verifying datasheet specs, and sizing isolation transformers for safety-critical applications. It’s especially helpful for validating voltage scaling before prototyping or performing thermal and wire gauge analysis.

These are the number of wire windings on the transformer’s primary (input) and secondary (output) coils. Turns directly determine voltage and current scaling: more secondary turns than primary yields step-up operation; fewer yields step-down. Real-world designs also consider core saturation, winding resistance, and leakage inductance—but this tool assumes ideal conditions.

Load power enables calculation of both secondary and primary currents using P = V × I, assuming unity power factor and lossless operation. This avoids ambiguity when load impedance isn’t known—common in preliminary design. For non-unity PF or reactive loads, engineers should adjust results manually or use a more advanced AC analysis tool.

Primary/secondary turns typically range from 1–10,000+ depending on application (e.g., 50–500 for 120 V → 12 V power transformers). Primary voltage spans 3.3 V (low-voltage logic) to 480 V (industrial). Load power ranges from milliwatts (signal isolation) to several kilowatts—though accuracy degrades above ~5 kW without accounting for losses and thermal limits.

This occurs if you’ve entered N_s < N_p (fewer secondary turns), which inherently produces a step-down transformer—even if your primary voltage is low. The classification depends solely on the turns ratio: N_p/N_s < 1 ⇒ step-up; > 1 ⇒ step-down; = 1 ⇒ isolation. Double-check your turn counts and ensure units (turns, not layers or taps) are consistent.

No—this calculator models only two-winding, isolated transformers. Autotransformers share a common winding and require different equations for voltage/current relationships. Center-tapped configurations can be approximated by treating each half as a separate secondary, but the tool won’t compute tap-specific parameters like balanced load current or regulation.

First verify all inputs are positive, non-zero numbers—zero turns or voltage will cause division errors. Ensure primary and secondary turns reflect actual winding counts (not wire length or gauge). If calculated secondary current exceeds wire ampacity, revisit assumptions: real transformers need derating for losses, temperature rise, and skin effect—use this tool only for first-order estimation.

No—it assumes an ideal transformer with 100% efficiency, zero winding resistance, infinite core permeability, and perfect magnetic coupling. For practical design, apply 90–98% efficiency correction factors manually, or use dedicated transformer modeling software (e.g., SPICE with coupled inductors) when precision, thermal performance, or frequency response matters.

Impedance transforms as Z_s = Z_p × (N_s/N_p)². While this calculator doesn’t output impedance directly, you can compute it using the derived turns ratio. For example, a 10:1 step-down ratio reduces reflected load impedance by a factor of 100—critical for matching amplifiers to speakers or RF stages to antennas.