Single-Phase & Three-Phase

Transformer kVA Calculator

Calculate kVA, current or voltage from two known values. Then ask our team to check the transformer you need.

Use the calculator

Calculation Formulas

How the kVA calculation works

kVA measures apparent power. Use these formulas for a single-phase supply or a balanced three-phase system.

Single-Phase

kVA = V × A ÷ 1,000

Voltage multiplied by current, divided by 1,000

230 V × 10 A = 2.3 kVA

Three-Phase

kVA = √3 × V × A ÷ 1,000

Use line-to-line voltage and line current.

400 V × 20 A × √3 = 13.86 kVA

Calculating current or voltage instead?

The calculator rearranges the same formula. Use the transformer’s rated kVA to estimate full-load current. Voltage and current must relate to the same side.

FindSingle-phaseBalanced three-phase
Current (A)kVA × 1,000 ÷ VkVA × 1,000 ÷ (√3 × V)
Voltage (V)kVA × 1,000 ÷ AkVA × 1,000 ÷ (√3 × A)

One kVA equals 1,000 VA. The voltage result describes the entered kVA and current; it does not select a supply voltage or transformer ratio.

Single-Phase and Three-Phase kVA calculator

Transformer kVA calculator
kVA
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V
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kVA

Enter the voltage and current from the same side of the transformer.

Enter the line-to-line voltage and line current from the same side of the transformer.

This calculation assumes a balanced load across all three phases.

Enter the kVA and voltage for the side of the transformer you want to calculate the current for.

To calculate full-load current, use the transformer’s rated kVA.

Enter the total three-phase kVA and line-to-line voltage for the side of the transformer you want to calculate the line current for.

This calculation assumes a balanced load across all three phases.

To calculate full-load current, use the transformer’s rated kVA.

Enter the kVA and current from the same side of the transformer.

Enter the total three-phase kVA and line current from the same side of the transformer. The result is the line-to-line voltage.

This calculation assumes a balanced load across all three phases.

Before you specify

The calculation is the starting point

Starting current, operating duty and installation conditions can change the transformer you need. Send us the details you have. We’ll check the application before confirming a specification and quote.

Discuss your requirements

A Majestic Project

When starting current changed the design

A customer’s long cable runs suffered voltage drops at switch-on. Majestic developed a low-inrush transformer for the application, avoiding additional suppression components.

Read the project

Questions

A couple of useful checks

No fixed margin is added. The calculation shows apparent power, current or voltage from your inputs. Load behaviour and the installation need checking before a transformer is selected.

Ask us to review it. A basic kVA calculation does not account for unequal phase loads, motor starting or harmonics from electronic equipment. Include any starting-current figures or equipment data sheets you have.