Reactive Power & VAR Calculator
Reactive power doesn't do any real work, but it's essential for maintaining grid voltage — and it has to come from somewhere. This calculator takes real power (MW), power factor, and whether that power factor is lagging (inductive, absorbing VARs) or leading (capacitive, supplying VARs), then reports the reactive power (MVAR) the load demands or supplies and the total apparent power (MVA) the grid must deliver. It's the grid-operations counterpart to our Power Factor Correction Calculator, which focuses on facility-level capacitor bank sizing and demand charge savings — and it pairs naturally with our Short Circuit Current Calculator for the fault-side of substation and interconnection planning.
The real (active) power delivered to the load — the power that actually does useful work.
The ratio of real power to apparent power. Enter a value between 0.5 and 1.0.
Most industrial and utility loads are lagging (inductive) due to motors and transformers. Leading power factor is less common and typically comes from lightly-loaded lines or capacitive equipment.
Lagging (inductive) — the load absorbs VARs from the grid
real power (MW) ÷ power factor
Results update live as you type. For planning and field-check estimates — always verify against applicable standards and equipment ratings.
How we calculate this →Reactive power doesn't do any real work, but it's essential for maintaining grid voltage -- and it has to come from somewhere. A 100 MW load at 0.90 lagging power factor requires 48.4 MVAR of reactive power support from the grid, pushing total apparent power delivery to 111.1 MVA. Utilities and grid operators actively manage this reactive power balance across the system, since insufficient VAR support in a region can lead to voltage collapse, while excess reactive power flow increases losses on transmission and distribution lines.
How reactive power and apparent power are calculated
Real, reactive, and apparent power form the fundamental power triangle of AC systems, and this calculator applies it from the grid-operations perspective — how much reactive power a load demands or supplies, and how much total apparent power the grid must deliver. Two quantities tie the calculation together.
Reactive Power (MVAR) = Real Power (MW) × tan(arccos(Power Factor)). The power factor is the cosine of the angle between real and apparent power in the power triangle, so arccos(power factor) recovers that angle and tan of it gives the ratio of reactive to real power. At the defaults — 100 MW and 0.90 power factor — arccos(0.90) ≈ 25.84°, tan(25.84°) ≈ 0.4843, so Reactive Power = 100 × 0.4843 = 48.4 MVAR. The power factor type (lagging or leading) does not change the magnitude — it changes the sign and the physical interpretation: a lagging (inductive) load absorbs that 48.4 MVAR from the grid, while a leading (capacitive) load supplies 48.4 MVAR back to the system.
Apparent Power (MVA) = Real Power (MW) ÷ Power Factor. Apparent power is the vector combination of real and reactive power — the total current-carrying burden on the grid, regardless of how much of it does useful work. At the defaults, Apparent Power = 100 ÷ 0.90 = 111.1 MVA. Equivalently, Apparent Power = √(Real Power² + Reactive Power²) = √(100² + 48.4²) ≈ 111.1 MVA, the same result via the Pythagorean form of the power triangle.
Two notes on the model. First, this calculator uses a single, balanced, sinusoidal power factor value — real loads are three-phase, may be unbalanced, and may include harmonic content addressed by IEEE 1459's generalized definitions; for those conditions a full power-quality analysis is required. Second, the leading/lagging distinction matters operationally: a lagging load draws VARs that generators, synchronous condensers, or capacitor banks must supply to hold voltage, while a leading load injects VARs that can raise voltage and may need absorption (reactors) under light load. Data sources: Real, reactive, and apparent power definitions and relationships from IEEE 1415 (IEEE Guide for Induction Machinery Maintenance Testing and Failure Analysis) and IEEE 1459 (IEEE Standard Definitions for the Measurement of Electric Power Quantities Under Sinusoidal, Non-sinusoidal, Balanced, or Unbalanced Conditions); power factor and leading/lagging behavior from power systems engineering textbooks and IEEE standards; reactive power requirements for voltage stability from NERC (North American Electric Reliability Corporation) grid operations standards and voltage stability studies; reactive power management and VAR support strategies from utility operations and grid operator technical reports; voltage collapse mechanisms and reactive power insufficiency from power system stability and protection literature. Verification: with defaults (100 MW, 0.90 PF, Lagging), Reactive Power = 48.4 MVAR, Apparent Power = 111.1 MVA.