What formula is used for single-phase circuits?

For a single-phase circuit: I = V / R (Ohm's law), then S(kVA) = V × I / 1000 = V² / (R × 1000). Multiply the voltage squared by the inverse of resistance and divide by 1000.

What formula is used for three-phase circuits?

For three-phase (line-to-line voltage V_LL and resistance R per phase): the phase voltage is V_LL / √3, phase current is V_phase / R, and total three-phase apparent power is S(kVA) = 3 × V_phase × I_phase / 1000 = V_LL² / (R × 1000).

Does this apply to reactive (inductive or capacitive) loads?

This calculator assumes a purely resistive load where impedance equals resistance. For inductive or capacitive loads, you must use the total impedance Z (in ohms) rather than just R, and the result represents volt-amperes rather than watts.

What is the difference between kVA and kW?

kVA is apparent power — the total power supplied by the source. kW is real (active) power that does useful work. For purely resistive loads, the power factor is 1, so kVA equals kW. For reactive loads, kW = kVA × power factor.

Why would I use resistance instead of current to find kVA?

Sometimes only the resistance of a load is known — for example, from a multimeter reading or a component datasheet — and the current has not been measured. Using V and R lets you derive the kVA without needing a current clamp.

What units should I use for resistance?

Enter resistance in ohms (Ω). If your value is in milliohms, divide by 1000 before entering. If it is in kilohms, multiply by 1000.

Ohms to kVA Calculator

Name: Ohms to kVA Calculator
Availability: InStock
Author: Nham Vu

Enter resistance in ohms and voltage to instantly calculate the apparent power in kilovolt-amperes (kVA).

Circuit Parameters

Circuit Type

Resistance (Ω)

Voltage (V) (line-to-neutral)

Result

Enter values and press Calculate

Formula Reference

Single-Phase AC

I = V / R

kVA = V × I / 1000

Equivalently: V² / (R × 1000)

Three-Phase AC (line-to-line V)

V_ph = V_LL / √3

kVA = V_LL² / (R × 1000)

R is resistance per phase

Result copied!

Summary

Enter resistance in ohms and voltage to instantly calculate the apparent power in kilovolt-amperes (kVA).

How it works

Select the circuit type: single-phase AC or three-phase AC.
Enter the resistance in ohms (Ω).
Enter the supply voltage in volts (V).
Click Calculate — the tool derives current using Ohm's law (I = V / R).
Apparent power is then computed: S = V × I and converted to kVA.
A detailed breakdown table shows every intermediate value and the formula used.

Use cases

Determine the apparent power drawn by a purely resistive load given its impedance.
Size transformers and generators for resistive heating elements.
Estimate kVA demand for electric furnaces, ovens, and resistance heaters.
Cross-check nameplate resistance values against rated kVA capacity.
Teach or study Ohm's law and apparent power relationships.
Verify circuit protection ratings for known resistive loads.
Compare single-phase vs. three-phase power delivery for the same resistance.
Quick field calculation when only a resistance measurement is available.

Frequently Asked Questions

Last updated: 2026-06-15 · Reviewed by Nham Vu