VA to Amps Calculator

About the VA to Amps Calculator

A VA to amps calculator converts apparent power in volt-amperes to current in amperes — essential for determining the actual current that will flow when connecting VA-rated equipment such as UPS systems, transformers, and power supplies to an electrical circuit. Every generator, transformer, and UPS system is rated in VA (or kVA), and when you connect one to a circuit, the current it draws depends on the supply voltage. Getting this wrong causes two types of problems: undersizing the circuit (leading to overloaded conductors and nuisance tripping) or oversizing it wastefully. Our free VA to amps calculator handles single-phase 120V and 240V circuits (US/CA), 230V single-phase (EU/UK/AU), and all standard three-phase voltages, providing both single-phase and three-phase results simultaneously for easy comparison. The three-phase result is particularly valuable for sizing the supply connection to commercial UPS systems, generator sets, and large transformers where three-phase feeds are standard. Used daily by data center engineers, facilities managers, and electrical contractors worldwide.

How It Works

Single-phase: A = VA / V. Three-phase: A = VA / (V × √3). Example 1 (UPS): 3,000 VA UPS operating at 120V: A = 3,000 / 120 = 25A (single-phase). This requires a dedicated 30A circuit (25A × 1.25 = 31.25A for continuous load) with 10 AWG conductors. At 240V: A = 3,000 / 240 = 12.5A. Example 2 (transformer): 75 kVA transformer at 208V three-phase: A = 75,000 / (208 × 1.732) = 75,000 / 360.25 = 208.2A per phase on the secondary side. Feeder sizing: 208.2A × 1.25 = 260.3A → 300A breaker and 350 kcmil conductors. Example 3 (EU UPS): 10 kVA UPS on 230V single-phase: A = 10,000 / 230 = 43.5A. UK Consumer Unit MCB: 50A Type C MCB in a sub-board.

Tips & Best Practices

• ✓UPS bypass current: UPS systems also draw input current to charge batteries and supply the load. Input current is typically slightly higher than output VA / input voltage due to UPS inefficiency (90-97% for modern double-conversion units). A 3,000 VA UPS at 95% efficiency draws 3,000 / 0.95 / 120 = 26.3A input at 120V.
• ✓Three-phase transformer connections: for a delta-wye transformer, primary and secondary current calculations differ because of the voltage transformation ratio and connection type. Always specify the connection (delta or wye) and line-to-line vs. line-to-neutral voltage when sizing feeders.
• ✓NEC Article 450 (transformers): transformers must be protected by overcurrent devices rated at 125% of the rated primary current for transformers 9 kVA and below. For larger transformers: 250% for overcurrent protection on the primary, provided there is secondary protection. Always consult the applicable code for exact requirements.

Who Uses This Calculator

Data center engineers sizing input power circuits for UPS systems based on VA ratings. Electricians sizing feeder conductors and overcurrent devices for transformer installations. IT managers verifying that existing circuits can support new UPS unit additions. Facilities personnel calculating the current draw of VA-rated equipment for load balancing across electrical panels.