Transformer Calculator

What this calculator does

The Transformer Calculator provides fast estimates using standard electrical relationships. Enter Load Power, Power Factor (PF), Design Margin to compute results for real-world electrical scenarios. Use it for quick checks, comparisons, and documentation while planning.

Inputs explained

  • Load Power: Power value as labeled (W, kW, VA, or kVA).
  • Power Factor (PF): Power factor for AC loads (0 to 1).
  • Design Margin: Value used by the calculator.
  • Primary Voltage: Electrical potential difference in volts (V).
  • Secondary Voltage: Electrical potential difference in volts (V).

How it works / Method

The calculator applies the listed formulas to the values you enter and then formats the result in standard units.

Formulas used

  • kVA = kW / PF
  • I = kVAx1000 / V
  • I = kVAx1000 / (sqrt(3)xV)

Units: P in watts (W) PF is unitless (0 to 1) V in volts (V)

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Transformer Sizing Calculator

Calculate transformer kVA and currents

kW
V
V
Result
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Formulas

kVAkVA = kW / PF
I (1φ)I = kVA×1000 / V
I (3φ)I = kVA×1000 / (√3×V)

Standard Sizes (kVA)

Single-Phase: 5, 10, 15, 25, 37.5, 50, 75, 100, 167, 250, 333, 500

Three-Phase: 15, 30, 45, 75, 112.5, 150, 225, 300, 500, 750, 1000, 1500, 2000, 2500

Related

kVA to AmpskW to kVAMotor Current

Step-by-step example

Scenario: A 240V to 12V step-down transformer with 480 primary turns.

Formula: Ns = Np x (Vs / Vp)

  1. Ns = 480 x (12 / 240)
  2. Ns = 480 x 0.05
  3. Ns = 24 turns

Result: 24 secondary turns

Use cases

  • Estimate motor or transformer current and sizing values.
  • Compare star vs delta relationships quickly.
  • Support preliminary equipment selection decisions.
  • Document assumptions for project planning.

Assumptions & limitations

  • Results are estimates and may be rounded; small differences are expected.
  • Inputs assume steady-state values; transient and surge effects are not modeled.
  • Voltage can vary by supply, load, and location; use measured values when possible.
  • Power factor varies by load type; use a realistic value for inductive equipment.
  • Wiring rules and safety codes vary by jurisdiction; consult a licensed electrician for installation decisions.

Sources & references

Related calculators

Frequently Asked Questions

The Transformer Calculator estimates electrical quantities for equipment systems. It uses standard relationships between voltage, current, and configuration. Results are useful for planning and documentation. Use nameplate values when available. This tool does not model losses or inrush. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Voltage, current, and configuration drive most results. Confirm line versus phase quantities. Use consistent units across all inputs. Small input errors can change the outcome. Validate with manufacturer data when possible. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

No, the calculator uses ideal relationships. Real equipment includes losses and temperature rise. Motors also have starting and inrush conditions. Use datasheets for efficiency and derating. Treat the output as a baseline estimate. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Results are accurate for ideal conditions and correct inputs. Power factor and harmonics can shift real values. Use measured values if accuracy is critical. Document assumptions used for the calculation. Validate with equipment data where possible. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

No. Installation decisions must follow local codes. Use manufacturer instructions for wiring and protection. Consult a licensed electrician or engineer. Use this tool for planning and comparison. Keep safety as the priority in all installations. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Three-phase systems require line-to-line voltage in most cases. Confirm whether the connection is star or delta. Formulas differ for line and phase quantities. Check configuration before interpreting results. Use equipment documentation to verify assumptions. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.