Transformer Sizing Calculator

Select the correct transformer kVA rating for your lighting or electrical load. Enter all loads, apply demand and growth factors, and get a recommendation from standard kVA sizes.

Voltage and configuration
Demand and growth factors
What % of connected load runs at once
Headroom for future loads
Loads
Load / circuitWatts (W)Qty
+ Add load

Please add at least one load with a valid wattage.

Recommended transformer size
0 kVA
0
kVA (minimum)
Too small
0
kVA (recommended)
Best choice
0A
Full load amps – primary
0A
Full load amps – secondary
Total connected load
Total VA (div power factor)
Demand VA (x demand factor)
Design VA (x growth factor)
Required kVA
Transformer loading at design
NEC 450.3 – Overcurrent protection (recommended transformer)
Primary OCPD (max)
Secondary OCPD (max)
Primary conductor ampacity
Secondary conductor ampacity
Load breakdown
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The calculators and tools on LightingCalc.lighting are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. LightingCalc.lighting makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.