📊 Free Tool

Amps to VA Calculator

Convert current in amps to apparent power in volt-amperes (VA) for single-phase and three-phase AC. Features kVA auto-display, UPS sizing recommendations, unit dropdowns, and equipment reference tables.

Apparent Power
600 VA
0.60 kVA

How to Convert Amps to VA

Converting amps to volt-amperes (VA) calculates the apparent power drawn from a power source—critical for sizing UPS systems, transformers, generators, and switchgear. Unlike watts, VA includes both real and reactive power components, making it the correct metric for equipment capacity planning.

1

Select Phase

Choose single-phase for most residential/office equipment, or three-phase for industrial and data center loads.

2

Enter Values

Input current (mA/A/kA) and voltage (V/kV). Results calculate automatically as you type.

3

Get VA + UPS Size

Result shows VA, kVA (for large values), UPS size recommendation (with 30% margin), and estimated watts at common power factors.

Amps to VA Formula

Single-Phase
S(VA) = I(A) × V(V)
Three-Phase
S(VA) = √3 × I(A) × V(V)
S = Apparent power (VA), V = Line-to-line voltage (3-phase)
The Power Triangle
S² = P² + Q²
S = Apparent power (VA) — total power from source
P = Real power (W) — useful power doing work
Q = Reactive power (VAR) — oscillating power in inductors/capacitors
PF = P / S (power factor, 0 to 1)

Example Calculations

Office Server Rack: 5A at 120V
S = 5 × 120 = 600 VA
Result: 600 VA → Use 1000 VA UPS
With 30% margin: 780 VA minimum. At PF=0.7: real power = 420W.
Home Office: 3A at 120V
S = 3 × 120 = 360 VA
Result: 360 VA → Use 500 VA UPS
Desktop + monitor + router. A 500VA UPS provides ~15 min backup.
Data Center PDU: 30A at 208V 3-Phase
S = 1.732 × 30 × 208 = 10,808 VA
Result: 10.8 kVA → Use 15 kVA UPS
A standard 30A three-phase PDU. At PF=0.9: real power ≈ 9.7 kW.
Industrial Motor: 50A at 480V 3-Phase
S = 1.732 × 50 × 480 = 41,569 VA
Result: 41.6 kVA
A 50HP motor. Requires a transformer rated ≥ 50 kVA to handle the load.
Transformer Sizing: 100A at 240V
S = 100 × 240 = 24,000 VA
Result: 24 kVA → Use 25 kVA transformer
Standard utility transformer for residential service. Provides up to 100A at 240V split-phase.

Amps to VA Conversion Table

Amps120V 1Φ208V 1Φ240V 1Φ208V 3Φ480V 3Φ
1A120 VA208 VA240 VA360 VA831 VA
5A600 VA1,040 VA1,200 VA1,801 VA4,157 VA
10A1,200 VA2,080 VA2,400 VA3,602 VA8,314 VA
20A2,400 VA4,160 VA4,800 VA7,204 VA16,627 VA
30A3,600 VA6,240 VA7,200 VA10,808 VA24,941 VA
50A6,000 VA10,400 VA12,000 VA18,013 VA41,569 VA

VA vs. Watts at Different Power Factors

This table shows how much real power (watts) is available from a given VA rating at various power factors. This is critical when selecting UPS systems, which have both VA and watt limits.

Apparent PowerPF = 0.6PF = 0.7PF = 0.8PF = 0.9PF = 1.0
500 VA300W350W400W450W500W
1,000 VA600W700W800W900W1,000W
1,500 VA900W1,050W1,200W1,350W1,500W
3,000 VA1,800W2,100W2,400W2,700W3,000W
5,000 VA3,000W3,500W4,000W4,500W5,000W
10,000 VA6,000W7,000W8,000W9,000W10,000W

Common Equipment VA Ratings

EquipmentTypical VATypical PFReal Power (W)Notes
LED Monitor (24")50–80 VA0.9547–76WEnergy Star rated
Desktop PC (office)250–400 VA0.85–0.99200–350WPFC improves PF
Gaming PC500–800 VA0.90–0.99450–750WPSU dependent
Network Switch (24-port)50–200 VA0.9045–180WPoE adds load
Rack Server (1U)500–1,500 VA0.90–0.98450–1,400WDual PSU common
Laser Printer (peak)500–1,800 VA0.60300–1,080WHigh startup surge
NAS (4-bay)100–200 VA0.8585–170WSpindle count matters
Window AC (10,000 BTU)1,200–1,500 VA0.80960–1,200WMotor PF varies
Transformer (50 kVA)50,000 VAN/ADepends on loadRated by VA, not watts

⚠️ UPS & Transformer Sizing Safety

  • Dual-limit rule: UPS systems have both VA and watt limits. You must stay below BOTH. A "1500VA/900W" UPS cannot supply more than 1500VA OR 900W—whichever is hit first. With PF=0.6 loads, the watt limit is rarely reached first.
  • Safety margin: Always size UPS 25-40% above calculated load. Batteries degrade over time (expect 80% capacity after 3 years). Running near capacity reduces runtime dramatically.
  • Transformer derating: Transformers are rated for continuous VA load. Harmonic-rich loads (servers, VFDs) require derating by 10-30%. A 100 kVA transformer serving IT equipment may only safely supply 70-80 kVA.
  • Three-phase balance: Balance loads evenly across all three phases. Phase imbalance exceeding 10% causes motor heating and can trip protection. Calculate VA per phase individually.

Understanding Apparent Power (VA)

Apparent power, measured in volt-amperes (VA), is the total power that flows from a power source to a load in an AC circuit. It is the product of RMS voltage and RMS current, regardless of their phase relationship. Understanding VA is essential for anyone working with UPS systems, transformers, generators, or any AC power distribution equipment.

The distinction between VA and watts confuses many people, but it is critically important. Real power (watts) does useful work—lighting bulbs, running computations, heating elements. Reactive power (VAR) flows back and forth between the source and reactive components (inductors in motors, capacitors in power supplies) without doing useful work. Apparent power (VA) is the vector sum of both. The power factor is the ratio: PF = W / VA.

For practical UPS and generator sizing, you must use VA, not watts. A generator rated at 10 kW with PF = 0.8 can supply up to 12.5 kVA. But if your load has PF = 0.6, the generator can supply only 10 kW / 0.6 = 16.67 kVA of apparent current—it would need to be rated for 16.67 kVA at the alternator level, which most 10 kW generators can handle (they're typically rated for 12.5 kVA). Always check both ratings.

For converting between watts and amps, use our Amps to Watts Calculator. To calculate AC wattage from voltage and current — including real power, apparent power, and reactive power breakdown — our AC Wattage Calculator provides the full power triangle for both single-phase and three-phase circuits. To find current from voltage, try our Volts to Amps Calculator. For transformer design, visit our Transformer Calculator.

Frequently Asked Questions

For single-phase AC: multiply amps by volts (VA = I × V). For three-phase: VA = √3 × I × V (where V is line-to-line voltage). VA stands for volt-amperes and measures apparent power—the total power drawn from the source. This differs from watts (real power) by the power factor: W = VA × PF.
VA (volt-amperes) is apparent power—total power drawn. Watts is real power—power that does useful work. They are equal only when power factor = 1 (resistive loads). For reactive loads (motors, UPS): VA > Watts. Example: a 1000VA UPS with PF=0.8 delivers only 800W of real power. Always check both ratings.
Apparent power (S) is the product of RMS voltage and RMS current in an AC circuit. Measured in VA or kVA, it represents the total power that must be supplied by the source (generator, transformer, UPS). It is the vector sum of real power (P, in watts) and reactive power (Q, in VAR): S² = P² + Q².
UPS systems are rated in both VA and watts. The VA rating limits the maximum current the UPS can supply. The watt rating limits the actual power. You must stay under BOTH limits. A 1500VA/900W UPS at 120V provides max 12.5A of current. If your load draws 11A at PF=0.7, that is 1320VA and 924W—exceeds the 900W limit even though 1320VA < 1500VA.
Step 1: Add up the VA of all connected devices (use amps × voltage). Step 2: Add 25-40% safety margin. Step 3: Choose a UPS with both sufficient VA and watt ratings. Example: server 4A + monitor 1A + router 0.5A at 120V = 660VA. With 30% margin: 858VA. Choose a 1000VA UPS minimum. Check watt rating too.
Power factor (PF) is the ratio of real power to apparent power: PF = W / VA. It ranges from 0 to 1 (or 0 to 100%). PF=1 means all power does useful work. PF=0.8 means only 80% does useful work; 20% flows back and forth as reactive power. Low PF wastes energy and requires oversized wiring/transformers. Utilities may charge penalties for PF below 0.85.
kVA stands for kilovolt-ampere, equal to 1,000 VA. It is commonly used for large equipment: transformers (25-2500 kVA), generators (50-2000 kVA), UPS systems (1-500 kVA), and industrial motors. A 100 kVA transformer at 240V can supply up to 416.7A. The real power delivery depends on load PF: 100 kVA × 0.85 PF = 85 kW.
Three-phase VA = √3 × V_LL × I, where V_LL is line-to-line voltage. For example: 30A at 480V three-phase = 1.732 × 480 × 30 = 24,941 VA (24.9 kVA). The √3 factor accounts for the 120° phase offset between the three phases. For line-to-neutral: VA = 3 × V_LN × I.
Desktop computer: 250-500 VA. Server: 500-1500 VA. Monitor: 50-150 VA. Network switch: 50-200 VA. Laser printer: 500-1800 VA (peak). Refrigerator: 100-400 VA. Air conditioner: 1200-3600 VA. The VA rating is usually higher than watts because most electronics have PF < 1.
Reactive power (Q, measured in VAR) is power that oscillates between source and load without doing work. It comes from inductors (motors, transformers) and capacitors. The power triangle relates them: S² = P² + Q², where S is apparent power (VA), P is real power (W), Q is reactive power (VAR). Reactive power increases VA without increasing useful work.

Related Calculators

💪

Amps to Watts Calculator

Convert amps to real power (watts) for DC and AC.

 ⚡

AC Wattage Calculator

Calculate real power (W), apparent power (VA), and reactive power (VAR) for AC circuits.

 ⚙️

Volts to Amps Calculator

Find current from voltage using watts or resistance.

 🔄

Transformer Calculator

Size transformers with voltage, current, and turns ratio.