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Free transformer sizing calculator & electrical transformer calculator. Calculate power ratings, efficiency, impedance, voltage regulation, and electrical parameters with step-by-step solutions for power distribution and industrial applications.
Last updated: February 2, 2026
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4.80
kVA
4.00
N₁/N₂
95.0
%
4800.00
%
Given: Primary voltage = 480 V, Primary current = 10 A, Secondary voltage = 120 V
Step 1: Calculate turns ratio N = V₁/V₂ = 480/120 = 4.00
Step 2: Calculate secondary current I₂ = (V₁ × I₁)/V₂ = (480 × 10)/120 = 40.00 A
Step 3: Calculate power rating P = V₁ × I₁ = 480 × 10 = 4800 VA = 4.80 kVA
Step 4: Calculate efficiency η = 95% (typical for distribution transformers)
Step 5: Calculate losses = P × (100 - η)/100 = 4800 × (100 - 95)/100 = 240 W
Step 6: Calculate impedance Z = (V₁²/P) × 100 = (480²/4800) × 100 = 4800.00%
Power Rating
P = V × I
Turns Ratio
N = V₁/V₂
Efficiency
η = (P_out/P_in) × 100%
Impedance
Z = V²/P
Best for
Load sizing
Calculate power rating from primary/secondary voltage and current values
Best for
Loss analysis
Determine efficiency, core losses, and copper losses
Best for
System analysis
Calculate impedance percentage and voltage regulation effects
Best for
Load matching
Size transformer based on secondary current requirements
Application
Power distribution
Optimized for utility and commercial distribution systems
Application
Industrial systems
Designed for manufacturing and heavy industrial applications
For transformer: 480V primary, 120V secondary, 10A primary current
Power Rating
4.8 kVA
Secondary Current
40 A
Our transformer sizing calculator uses electrical engineering principles and transformer theory to calculate power ratings, efficiency, impedance, and other critical parameters. The calculator applies fundamental electrical laws to ensure proper transformer sizing for power distribution and industrial applications.
Power Rating: P = V × I (single-phase)Power Rating: P = √3 × V × I (three-phase)Efficiency: η = (P_out/P_in) × 100%Impedance: Z = (V²/P) × 100%These fundamental formulas form the basis of transformer sizing calculations. The calculator considers efficiency, losses, and impedance to provide accurate sizing recommendations for various applications.
Shows primary and secondary windings with electrical parameters
Transformer sizing is based on electrical engineering principles including electromagnetic theory, power system analysis, and energy conversion. The fundamental transformer equation relates primary and secondary voltages to the turns ratio, while power conservation principles determine current relationships.
Need help with other electrical calculations? Check out our capacitor calculator and joules calculator.
Get Custom Calculator for Your PlatformResult: 4.8 kVA transformer with 40 A secondary current
The transformer can handle 4.8 kVA of load with 95% efficiency and 240 W total losses.
5 kVA transformer with 96% efficiency
Losses = 200 W (4% of 5 kVA)
Core losses = 80 W, Copper losses = 120 W
10 kVA, 480V transformer with 5% impedance
Voltage regulation = 3%
Fault current = 20 times full-load current
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