Transformer Winding Calculator
Calculate transformer winding turns, wire gauge, and core area.
Design custom transformers for power supplies, audio, and isolation applications.
A transformer transfers electrical energy between circuits using electromagnetic induction. It consists of two or more coils (windings) wound around a common magnetic core. The ratio of turns between the primary and secondary winding determines the voltage transformation ratio.
The fundamental transformer equations:
Turns ratio: N₁/N₂ = V₁/V₂ = I₂/I₁
Where N₁ and N₂ are turns in primary and secondary, V₁ and V₂ are voltages, and I₁ and I₂ are currents.
To calculate secondary turns: N₂ = N₁ × (V₂ / V₁)
For a power transformer core, the required primary turns (Np) using the core area method: Np = (V × 10⁸) / (4.44 × f × Bmax × Ac)
Where:
- V = primary voltage (volts)
- f = frequency (Hz) — typically 50 or 60 Hz
- Bmax = maximum flux density (Tesla) — typically 1.2–1.5 T for silicon steel laminations
- Ac = effective core cross-section area (cm²)
- 4.44 = waveform factor for sinusoidal AC (4π / √2)
Wire gauge is determined by current density. A safe current density for copper wire in a transformer is 3–4 A/mm² (this depends on cooling). For a given current, you calculate the minimum wire cross-sectional area: Area (mm²) = Current (A) / Current Density (A/mm²)
AWG and metric wire equivalents at 3 A/mm²:
- 1A → ~0.33 mm² → AWG 22 (0.64 mm dia)
- 2A → ~0.67 mm² → AWG 20 (0.81 mm dia)
- 5A → ~1.67 mm² → AWG 15 (1.45 mm dia)
- 10A → ~3.33 mm² → AWG 12 (2.05 mm dia)
Transformer efficiency is typically 90–98% for well-designed units. The power output equals primary power × efficiency. Core losses (hysteresis and eddy currents) and copper losses (I²R heating in wires) reduce efficiency.
This calculator helps with the turns ratio and wire sizing aspects of transformer design. Core sizing and detailed magnetics require additional calculations beyond this tool.