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Capacitor kVAR Calculator

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Calculate capacitor bank kVAR required for power factor correction, capacitor capacitance, corrected power factor, current reduction and kVA reduction for single-phase and three-phase AC systems.

Inputs

1

System configuration

Choose the AC system and the type of capacitor calculation you want to perform.

2

Load and power factor

These values determine the reactive power that must be compensated.

Enter the actual real power consumed by the load. For motors, use input electrical power rather than shaft output power.

Single phase: line-to-neutral voltage. Three phase: line-to-line voltage.

Use the measured operating power factor whenever possible. Motor nameplate PF may differ from actual site PF.

Typical design targets are often around 0.95–0.99 depending on utility requirements, load profile and harmonic conditions.

Optional additional kVAR allowance. Avoid excessive margin because over-correction can create leading power factor.

3

Capacitor bank

Use these values when checking an existing capacitor or planning an APFC bank.

Used when calculating capacitance from a known capacitor-bank kVAR.

Enter capacitance of one capacitor unit. For three-phase systems this is per phase/unit.

For three-phase capacitor banks, choose the actual capacitor connection. Delta and star have different voltage across each capacitor.

Number of switching stages in an automatic power factor correction bank.

4

Optional demand analysis

Enter your demand tariff if you want an indicative monthly kVA-demand saving.

Optional. Enter your utility demand-charge rate to estimate monthly kVA-demand savings.

How to use this calculator: Capacitor kVAR Calculator

Calculate capacitor bank kVAR required for power factor correction, capacitor capacitance, corrected power factor, current reduction and kVA reduction for single-phase and three-phase AC systems. The example below is calculated by this page's real engine from the displayed inputs.

  1. 1Confirm that the Capacitor kVAR Calculator matches the quantity or design check you need.
  2. 2Enter Real load power, System voltage, and Existing power factor using the units printed beside each field.
  3. 3Select the applicable Electrical system, Calculation mode, and Frequency options; these choices change the calculation method or factors.
  4. 4Calculate, then follow the substituted equations in the worked example and compare the result with any stated limit.
  5. 5Read the assumptions, warnings and cited references before using the result for a financial, medical or engineering decision.

Input guide and example values

Use values from the same measurement basis and time period. Conditional fields appear only when the related option is selected.

InputExample valueWhy it matters
Electrical systemThree phase ACSelect the option that matches the real installation or scenario.
Calculation modeRequired capacitor kVAR from power factorSelect the option that matches the real installation or scenario.
Real load power100 kWEnter the actual real power consumed by the load. For motors, use input electrical power rather than shaft output power.
System voltage415 VSingle phase: line-to-neutral voltage. Three phase: line-to-line voltage.
Frequency50 HzSelect the option that matches the real installation or scenario.
Existing power factor0.8Use the measured operating power factor whenever possible. Motor nameplate PF may differ from actual site PF.
Target power factor0.95Typical design targets are often around 0.95–0.99 depending on utility requirements, load profile and harmonic conditions.
Design margin0 %Optional additional kVAR allowance. Avoid excessive margin because over-correction can create leading power factor.
Capacitor bank50 kVARUsed when calculating capacitance from a known capacitor-bank kVAR.
Capacitance per capacitor100 µFEnter capacitance of one capacitor unit. For three-phase systems this is per phase/unit.
Capacitor connectionDeltaFor three-phase capacitor banks, choose the actual capacitor connection. Delta and star have different voltage across each capacitor.
APFC capacitor steps6Number of switching stages in an automatic power factor correction bank.
Demand charge0 ₹/kVA/monthOptional. Enter your utility demand-charge rate to estimate monthly kVA-demand savings.

Formula, derivation and worked example

This capacitor kVAR calculator is designed for practical power-factor-correction studies in residential, commercial and industrial AC systems. It calculates the reactive power currently drawn by a load, the reactive power corresponding to the target power factor, the capacitor-bank kVAR required between those two conditions, the resulting corrected kVA and current, and the corresponding capacitor capacitance. It supports both single-phase and balanced three-phase systems and distinguishes star and delta capacitor connections.

Required capacitor kVAR: Qc = P × [tan(cos⁻¹ PF₁) − tan(cos⁻¹ PF₂)]
Existing reactive power: Q₁ = P × tan(cos⁻¹ PF₁)
Target reactive power: Q₂ = P × tan(cos⁻¹ PF₂)
Apparent power: S = √(P² + Q²)
Single-phase current: I = P × 1000 / (V × PF)
Three-phase current: I = P × 1000 / (√3 × VLL × PF)
Single-phase capacitor: Q = 2πfCV² / 1000
Three-phase star capacitor: Q = 2πfCVLL² / 1000
Three-phase delta capacitor: Q = 3 × 2πfCVLL² / 1000

Substitution steps

  1. 1. Existing reactive power
    Q₁ = P × tan(cos⁻¹ PF₁)
    = 75 kVAR
  2. 2. Target reactive power
    Q₂ = P × tan(cos⁻¹ PF₂)
    = 32.868 kVAR
  3. 3. Required compensation
    Qc = Q₁ − Q₂
    = 42.132 kVAR
  4. 4. Design-margin compensation
    Qc × (1 + margin/100)
    = 42.132 kVAR
  5. 5. Practical capacitor bank
    next available standard bank size
    = 50 kVAR
  6. 6. Corrected reactive power
    Qcorrected = Q₁ − Qc
    = 25 kVAR
  7. 7. Corrected apparent power
    S = √(P² + Q²)
    = 103.078 kVA
  8. 8. Corrected current
    I = P × 1000 / (√3 × VLL × PF)
    = 143.402 A
  9. 9. Capacitance
    C = Q / (3ωVLL²)
    = 308.037 µF

Computed example results

Recommended capacitor bank
50 kVAR
theoretical 42.13 kVAR
Theoretical required compensation
42.13 kVAR
before optional design margin
Existing reactive power
75 kVAR
Target reactive power
32.87 kVAR
Corrected power factor
0.9701
✅ Very good — target achieved
Power factor condition
Lagging
Existing apparent power
125 kVA
Corrected apparent power
103.08 kVA
reduction 17.5%
Existing line current
173.9 A
Corrected line current
143.4 A
current reduction 17.5%
Capacitor current
69.56 A
Capacitor kVAR per phase
16.67 kVAR
Recommended APFC step
8.33 kVAR/step
6 switching steps
Capacitance per capacitor
308.04 µF
delta connection
Estimated monthly demand saving
Enter demand charge
optional estimate

Understanding the result

Read the main result together with supporting checks, assumptions, limits and intermediate values.

For a manual check, repeat the first equation, confirm the units and change one input at a time.

Common mistakes when using Capacitor kVAR Calculator

  • Do not mix units for Real load power (kW), System voltage (V), Design margin (%). A unit mismatch changes the input magnitude even when the typed number looks reasonable.
  • Do not leave Electrical system on the default choice unless that choice matches the real scenario; the selected option can change the calculation path or factor.
  • Do not replace the displayed Required capacitor kVAR: Qc = P × [tan(cos⁻¹ PF₁) − tan(cos⁻¹ PF₂)] relationship with a different convention without also changing the underlying assumptions; compare like-for-like methods when checking the result.
  • Do not treat Recommended capacitor bank = 50 kVAR from the worked example as a universal answer. It belongs to the displayed example inputs and must be recalculated for the actual case.

When the Capacitor kVAR Calculator is useful

Capacitor kVAR Calculator is designed for cases where Electrical system, Calculation mode, Real load power, System voltage are known and you need Recommended capacitor bank, Theoretical required compensation, Existing reactive power. The page keeps the live calculator, calculation method and worked example together so the result can be checked instead of treated as a black-box number.

Use the calculator for the scope described by its inputs and notes. The displayed method is Required capacitor kVAR: Qc = P × [tan(cos⁻¹ PF₁) − tan(cos⁻¹ PF₂)]. If the real project or decision needs factors that are not represented here, treat the result as an estimate and add the missing checks separately.

Electrical system and Calculation mode: what changes the answer

The worked example uses Electrical system = Three phase AC, Calculation mode = Required capacitor kVAR from power factor, Real load power = 100 kW, System voltage = 415 V. With those values, Recommended capacitor bank is 50 kVAR. Changing an input should be interpreted according to that field's unit, range, option and hint rather than by the number alone.

For this calculator, the main input roles are: Electrical system: Select the option that matches the real installation or scenario. Available choices include Single phase AC, Three phase AC. Calculation mode: Select the option that matches the real installation or scenario. Available choices include Required capacitor kVAR from power factor, Capacitor kVAR from capacitance, Capacitance from capacitor kVAR. Real load power (kW): Enter the actual real power consumed by the load. For motors, use input electrical power rather than shaft output power. System voltage (V): Single phase: line-to-neutral voltage. Three phase: line-to-line voltage.

How to sanity-check a Capacitor kVAR Calculator result

Start by confirming the entered values and units, then compare the substituted working with the displayed formula or calculation steps. Pay particular attention to Recommended capacitor bank, because it is the first worked-example output shown by the live engine.

Finally, compare the result with the assumptions, warnings and related calculators on this page. A nearby calculator can be useful as a cross-check when it measures the same workflow from a different input or output direction.

Next logical calculator

Continue with 1-Phase / 3-Phase Power Calculator

Useful next check because both tools use Electrical system, while 1-Phase / 3-Phase Power Calculator answers a different part of the same workflow.

Open 1-Phase / 3-Phase Power Calculator

Formula

  • Required capacitor kVAR: Qc = P × [tan(cos⁻¹ PF₁) − tan(cos⁻¹ PF₂)]
  • Existing reactive power: Q₁ = P × tan(cos⁻¹ PF₁)
  • Target reactive power: Q₂ = P × tan(cos⁻¹ PF₂)
  • Apparent power: S = √(P² + Q²)
  • Single-phase current: I = P × 1000 / (V × PF)
  • Three-phase current: I = P × 1000 / (√3 × VLL × PF)
  • Single-phase capacitor: Q = 2πfCV² / 1000
  • Three-phase star capacitor: Q = 2πfCVLL² / 1000
  • Three-phase delta capacitor: Q = 3 × 2πfCVLL² / 1000

This capacitor kVAR calculator is designed for practical power-factor-correction studies in residential, commercial and industrial AC systems. It calculates the reactive power currently drawn by a load, the reactive power corresponding to the target power factor, the capacitor-bank kVAR required between those two conditions, the resulting corrected kVA and current, and the corresponding capacitor capacitance. It supports both single-phase and balanced three-phase systems and distinguishes star and delta capacitor connections.

Formulas explained

Qc = P × [tan(cos⁻¹ PF₁) − tan(cos⁻¹ PF₂)]

Power-factor correction does not change the real kW consumed by the load. The capacitor supplies part of the reactive power locally, reducing the reactive power that must come from the upstream source.

Qc
Required capacitor compensation in kVAR
P
Real load power in kW
PF₁
Existing power factor
PF₂
Target power factor

Q = P × tan(cos⁻¹ PF)

This converts real power and power factor into the reactive power associated with the load.

Q
Reactive power in kVAR
P
Real power in kW
PF
Power factor

S = √(P² + Q²)

Apparent power is the vector combination of real and reactive power. Improving power factor reduces Q and therefore reduces the kVA demand seen by the supply.

S
Apparent power in kVA
P
Real power in kW
Q
Reactive power in kVAR

I = P × 1000 / (√3 × VLL × PF)

For a balanced three-phase system, the line current required for a fixed kW load decreases as power factor improves.

I
Line current in A
VLL
Line-to-line voltage in V
PF
Power factor

Q = 2πfCV² / 1000

The reactive power of an AC capacitor depends on frequency, capacitance and the RMS voltage applied across the capacitor.

Q
Capacitive reactive power in kVAR
f
Frequency in Hz
C
Capacitance in farads
V
RMS voltage across the capacitor

What is capacitor kVAR?

Capacitor kVAR is the reactive power supplied locally by a capacitor bank. The capacitor offsets part of the inductive reactive power drawn by motors, transformers and other inductive loads, reducing the reactive current supplied by the upstream network.

Why install a capacitor bank?

Power-factor correction can reduce upstream current and kVA demand for the same real kW load. This can release capacity in cables, transformers and switchgear and may reduce utility demand-related charges where applicable.

How much kVAR do I need?

The required compensation depends on real power and the difference between the existing and target power factors. The standard calculation is Qc = P × [tan(cos⁻¹ PF₁) − tan(cos⁻¹ PF₂)].

kW vs kVAR vs kVA

kW is real power, kVAR is reactive power and kVA is apparent power. They form the power triangle: kVA² = kW² + kVAR². Power factor is kW/kVA.

Why does PF correction reduce current?

For a fixed real-power load, current is inversely proportional to power factor. Raising PF from 0.80 to 0.95 therefore reduces the current required from the source without reducing the useful kW load.

Star vs delta capacitor connection

In a three-phase delta bank each capacitor is exposed to the full line-to-line voltage. In a star bank each capacitor sees line voltage divided by √3. Therefore the capacitance required per capacitor is different for the same total kVAR.

Why APFC steps are useful

A fixed capacitor can over-correct a variable load. An automatic power-factor-correction panel switches capacitor stages according to the instantaneous reactive-power requirement so that compensation follows the load.

Harmonics and capacitor banks

Capacitors can interact with system inductance and harmonic currents. Where significant nonlinear loads, VFDs, UPS systems, rectifiers or harmonic distortion exist, a harmonic study and appropriately designed detuned or filtered capacitor bank may be required.

1-Phase / 3-Phase Power Calculator

Calculate kW, kVA, kVAR, current and power factor for single-phase and three-phase AC systems.

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Worked example

  1. 1Example: 100 kW three-phase load at 415 V, existing PF 0.80, target PF 0.95.
  2. 2Existing reactive power: Q₁ = 100 × tan(cos⁻¹ 0.80) = 75.0 kVAR.
  3. 3Target reactive power: Q₂ = 100 × tan(cos⁻¹ 0.95) ≈ 32.87 kVAR.
  4. 4Required compensation: Qc = 75.0 − 32.87 = 42.13 kVAR.
  5. 5The next practical bank size from the calculator's standard series is 50 kVAR.
  6. 6Before correction: kVA = 100 / 0.80 = 125 kVA and current ≈ 173.7 A at 415 V three phase.
  7. 7At the ideal 0.95 target: kVA = 100 / 0.95 ≈ 105.3 kVA and current ≈ 146.1 A.
  8. 8The capacitor therefore reduces upstream kVA and current for the same 100 kW real load.

Assumptions

  • AC RMS voltage and frequency are used.
  • Three-phase calculations assume a balanced system.
  • Three-phase voltage is line-to-line voltage.
  • Power factor is treated as a displacement power factor for the core calculation.
  • The load is assumed to be inductive/lagging for normal capacitor correction.
  • Real power remains approximately unchanged by ideal reactive compensation.
  • The calculated capacitor bank size is preliminary sizing; manufacturer capacitor ratings, voltage class, tolerances, temperature, switching duty and protection must be checked before installation.
  • For harmonic-rich installations, capacitor-reactor interaction must be assessed separately.

Tips

  • Use measured kW and PF from a power-quality meter when available instead of relying only on nameplate values.
  • For a variable industrial load, APFC is usually more appropriate than one permanently connected fixed capacitor bank.
  • Avoid selecting a capacitor bank substantially larger than the calculated requirement because excessive compensation can produce leading PF.
  • For 415 V three-phase systems, always use 415 V as line-to-line voltage in the √3 power equation.
  • Improving PF reduces current and kVA demand but does not directly reduce the real kWh consumed by an ideal load.
  • If the installation contains substantial VFD, UPS or rectifier loads, investigate harmonics before connecting conventional capacitors.

Warnings

  • Do not install a capacitor bank solely from this calculator without checking the actual site load profile, measured power factor and utility requirements.
  • Do not intentionally over-correct into a leading power factor unless the electrical system has been specifically designed for it.
  • VFDs, UPS systems, rectifiers, solar inverters and other nonlinear loads can create harmonics. A detuned reactor or harmonic filter may be required.
  • Capacitor switching equipment must be selected for capacitor inrush current and repetitive switching duty.
  • The capacitor voltage rating must be suitable for the actual system voltage and connection arrangement.
  • Final capacitor-bank protection, contactors, fuses, reactors, discharge resistors and cable sizing require a complete engineering check.

Standards & references

  • IEC 60831 — Shunt power capacitors of the self-healing type for AC power systems
  • IEC 61921 — Power capacitors: low-voltage power factor correction banks
  • IEC 61000 — Electromagnetic compatibility and harmonic considerations
  • IEC 60364 — Low-voltage electrical installations

Frequently asked questions

How do I calculate capacitor kVAR for power factor correction?

Use Qc = P × [tan(cos⁻¹ PF₁) − tan(cos⁻¹ PF₂)], where P is load power in kW, PF₁ is the existing power factor and PF₂ is the target power factor. The result is the required capacitor compensation in kVAR.

How much capacitor kVAR is required for 100 kW from 0.80 to 0.95 PF?

For 100 kW, 0.80 existing PF and 0.95 target PF, the theoretical compensation is approximately 42.1 kVAR. A practical bank would normally be selected from an available standard rating and checked against the actual load profile.

What is the difference between kW and kVAR?

kW represents real power that performs useful work. kVAR represents reactive power associated with electric and magnetic fields. kVA is the vector combination of kW and kVAR.

What capacitor size do I need for a 3-phase motor?

The capacitor size depends on the motor's real input power, actual operating power factor and desired target PF. Use measured operating values whenever possible rather than sizing only from the motor nameplate.

How do I calculate capacitor kVAR from capacitance?

For a single-phase capacitor, Q = 2πfCV². For a three-phase star-connected bank using line-to-line voltage, total Q = 2πfCVLL². For a three-phase delta-connected bank, total Q = 3 × 2πfCVLL². Convert VAR to kVAR by dividing by 1000.

Does power factor correction reduce electricity consumption?

Ideal power-factor correction does not remove the real kW energy required by the load. It primarily reduces reactive current and apparent-power demand. Actual kWh savings depend on the system losses and the particular installation.

Does improving power factor reduce current?

Yes. For the same real kW load and system voltage, current decreases as power factor increases. This can reduce upstream conductor, transformer and switchgear loading.

Should I use a fixed capacitor or APFC panel?

A fixed capacitor can suit a relatively constant inductive load. For variable loads, an APFC bank with switched stages can follow the changing reactive-power requirement and reduce the risk of over-correction.

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