Transformer kVA Calculator
Accurately calculate transformer capacity for single-phase and three-phase electrical systems with our easy-to-use tool.
Use this calculator to determine the required kVA rating for your transformer based on voltage and current values.
Calculation Result
Calculation Formulas
Single-Phase Transformer
kVA = (V × A) / 1000
Where V is voltage and A is current
Three-Phase Transformer
kVA = (√3 × V × A) / 1000
Where √3 ≈ 1.732, V is line-to-line voltage, and A is current
Transformer kVA Calculation Guide
Learn how to calculate transformer kVA ratings step by step for different electrical systems.
What is kVA?
kVA (kilovolt-amperes) represents the apparent power in an electrical system. It includes both real power (kW) and reactive power (kvar). Think of it as the total capacity required to run electrical equipment, similar to the total size of a container that holds both useful items and packaging.
For transformers, kVA rating indicates the maximum power the transformer can handle without overheating.
Step-by-Step Calculation Process
Identify the System Type
Determine if your electrical system is single-phase or three-phase. Residential systems are typically single-phase, while commercial and industrial systems often use three-phase.
Gather Required Values
You'll need:
- Voltage (V) of the system
- Current (A) drawn by the load
- For three-phase systems, remember the √3 (1.732) multiplier
Apply the Appropriate Formula
Use the formula corresponding to your system type:
Single-phase:
kVA = (V × A) / 1000
Three-phase:
kVA = (√3 × V × A) / 1000
Calculate and Select Transformer
Perform the calculation and select a transformer with a kVA rating equal to or greater than your result. It's recommended to add a safety margin of 20-25% for future expansion.
Practical Examples
Single-Phase Example
A 240V system with a 50A load:
kVA = (240V × 50A) / 1000
kVA = 12,000 / 1000 = 12 kVA
A 15kVA transformer would be appropriate (providing a safety margin).
Three-Phase Example
A 480V three-phase system with a 30A load:
kVA = (1.732 × 480V × 30A) / 1000
kVA = (1.732 × 14,400) / 1000
kVA = 24,940.8 / 1000 = 24.94 kVA
A 30kVA transformer would be appropriate (providing a safety margin).
Applications of Transformer kVA Calculations
Learn how to apply kVA calculations in various real-world scenarios.
Generator Sizing
Calculate the required generator kVA rating based on your load requirements using the formula:
kVA = kW / PF
Where PF is the power factor (typically 0.8 for many generators).
UPS Systems
For uninterruptible power supplies, calculate kVA load with a buffer:
UPS kVA = Load kVA × 1.3-1.6
The buffer accounts for inrush currents and future expansion.
Residential Loads
Sum all major electrical loads and apply demand factors:
- Lighting: 100-300 VA per room
- Appliances: Check nameplate ratings
- HVAC: Major load, check specifications
Use demand factors (typically 0.7-0.8) for total load.
Commercial Buildings
Calculate based on usage patterns and multiple load types:
- Office equipment: 50-100 VA per sq ft
- Retail: 100-200 VA per sq ft
- Warehouses: 25-50 VA per sq ft
Include safety margins for peak demand periods.
Industrial Applications
Account for heavy machinery and motor loads:
kVA = (HP × 0.746) / (Efficiency × PF)
Where HP is horsepower, typically with 1.5-2x multiplier for starting currents.
Renewable Energy
Size transformers for solar and wind systems:
- Solar: Match inverter output rating
- Wind: Account for variable output
- Include battery system considerations
Typically oversized by 10-15% for efficiency.
Transformer kVA Sizing by Application
Frequently Asked Questions
Find answers to common questions about transformer kVA calculations.