kVA to Current & Current to kVA Calculator

kVA to Amps formula (three-phase): I = (kVA × 1000) ÷ (1.732 × V) — for example, a 100 kVA transformer at 415 V draws roughly 139 A. Converting between apparent power (kVA) and current (Amps) is a conversion used constantly when sizing cables, breakers, transformers, and generators, or when cross-checking a nameplate's kVA rating against a measured current draw. Apparent power and current are directly related through voltage, but the exact relationship depends on whether the supply is single-phase or three-phase, because three-phase systems share the load across three conductors rather than two.

In a single-phase system, apparent power is simply the product of voltage and current: kVA = (V × I) / 1000. Rearranged, current can be found from a known kVA value as I = (kVA × 1000) / V. In a three-phase system, the same relationship includes a √3 (approximately 1.732) factor, because the line current in a balanced three-phase system relates to power differently than in single-phase: kVA = (√3 × V × I) / 1000, and conversely I = (kVA × 1000) / (√3 × V). This √3 factor is one of the most frequently used constants in electrical engineering and appears in nearly every three-phase power, current, or sizing calculation.

Note that unlike a kW-current conversion, no power factor is needed here — apparent power (kVA) already represents the total power flowing through a circuit regardless of how much of it is real versus reactive, so it converts to current using voltage alone.

Worked example: Suppose a three-phase distribution panel is rated at 415 V and the connected load draws 80 A. The apparent power demand is kVA = (1.732 × 415 × 80) / 1000 ≈ 57.5 kVA — useful for checking against the upstream transformer or generator's rated capacity. Conversely, if a 100 kVA transformer needs its full-load three-phase current checked at 415 V: I = (100 × 1000) / (1.732 × 415) ≈ 139.1 A, the figure used to size the main breaker and outgoing cable from that transformer.

This tool is especially useful for technicians and engineers who have one known quantity — say, a transformer's kVA nameplate rating — and need the equivalent current to select the correct cable size or protective device, or who have measured current draw and need to express it as an equivalent kVA demand for billing, generator sizing, or load-study purposes.

Single-Phase vs Three-Phase: Why the Formula Differs

A single-phase supply delivers power through a single live and neutral conductor, so the apparent power is simply the direct product of voltage and current. A three-phase supply instead delivers power across three conductors, each carrying current offset by 120° from the others. The √3 factor in the three-phase formula corrects for this phase offset — it's the same ratio that arises whenever line and phase quantities are related in a balanced three-phase system, and it means a three-phase circuit at a given voltage and kVA carries proportionally less current per conductor than an equivalent single-phase circuit would, since the load is effectively split three ways.

Common Mistakes When Converting kVA and Current

• Forgetting the √3 factor for three-phase systems. Applying the single-phase formula to a three-phase circuit overstates the current by a factor of 1.732, leading to an oversized cable or breaker recommendation.
• Using phase voltage instead of line voltage, or vice versa. Three-phase nameplates and utility connections are normally specified in line-to-line voltage (e.g. 415 V); mixing this up with the 230 V phase voltage produces a result off by √3.
• Confusing kVA with kW. A kVA to current conversion does not need a power factor, but a kW to current conversion does — using the wrong formula for the quantity you actually have will silently produce an incorrect current figure.
• Assuming balanced loading when it isn't. The three-phase formula assumes the load is evenly balanced across all three phases; a significantly unbalanced load will draw different current on each phase, and the calculated figure should be treated as an average, not a per-phase guarantee.

Quick Reference: Common kVA to Current Values

Figures rounded to 1 decimal place. Always verify against actual nameplate voltage before final cable or breaker selection.

kVA to Current Quick Reference Table (1-100 kVA)

Full kVA-to-current lookup from 1 to 100 kVA at the same two standard conditions used above — 230 V single-phase and 415 V three-phase — so you can read off the current without running the calculator for a common integer kVA rating.

Current to kVA Quick Reference Table (1-100 A)

The reverse lookup — every whole Amp value from 1 to 100 A, converted to the equivalent apparent power at 230 V single-phase and 415 V three-phase, useful for reading a breaker or cable current rating straight across to its kVA capacity.

Generator (DG Set) Sizing Notes

Diesel generators are almost always nameplated in kVA rather than kW, because the manufacturer is guaranteeing the alternator's current-carrying capacity rather than the engine's real power output — the two are only linked once a power factor is assumed. When selecting a DG set from a known load current, first convert that current to kVA using the three-phase formula above, then apply a safety margin. A common rule of thumb is to size the generator at 20–25% above the calculated running kVA to cover starting surges from motors, compressors, and other inductive loads, which can draw 3–6 times their running current for a second or two at startup.

For example, a factory with a steady three-phase load of 90 A at 415 V has a running demand of roughly kVA = (1.732 × 415 × 90) / 1000 ≈ 64.7 kVA. Adding a 25% margin for motor starting and future load growth points to a 75–80 kVA generator as a practical minimum, rather than one sized to the bare running figure. Undersizing a DG set to the exact calculated load is one of the most common site mistakes, since the set may run the steady load fine but stall or trip on protection every time a large motor starts.

Transformer Sizing Examples

Distribution transformers are rated in kVA on their nameplate together with primary and secondary voltage, and the current calculator above is the direct route from that rating to the full-load current on either winding. A 63 kVA transformer with a 415 V secondary has a full-load secondary current of about 87.7 A, which is the number used to select the secondary breaker and outgoing feeder cable. The same transformer's primary current is found the same way using the primary voltage instead — for an 11 kV primary, current = (63 × 1000) / (1.732 × 11000) ≈ 3.3 A, an order of magnitude lower because the primary operates at much higher voltage.

When a facility's total connected load is known only in kW, it must first be converted to kVA using the expected power factor (see the kW to kVA calculator) before this current formula can be applied, since a transformer's current-carrying limit is governed by kVA, not kW. Utilities and consultants commonly add 15–20% headroom above the calculated peak kVA demand when selecting a transformer size, to allow for load growth and to avoid running the unit continuously at its thermal limit.

Industrial Use Cases

• Panel and switchgear current verification. Site engineers use the kVA-to-current direction to cross-check that an incoming panel's bus bar and breaker rating actually covers the transformer or DG set feeding it, before energizing a new installation.
• Billing and demand monitoring. Utilities meter industrial consumers in kVA (apparent power) for demand charges; converting a measured current reading back to kVA lets a plant engineer track how close the site is running to its sanctioned load.
• Cable sizing for new feeders. Once the full-load current is known from a transformer or generator's kVA rating, it feeds directly into cable sizing tables (current-carrying capacity, derating for grouping and ambient temperature) to select the correct conductor cross-section.
• Parallel transformer and generator studies. When two or more transformers or DG sets run in parallel, engineers convert each unit's kVA rating to current at the common bus voltage to verify that combined current stays within the bus bar and protective device limits.