Power Factor Correction Calculator
Find the capacitor kVAR to improve power factor.
Results update as you type.
How it works
A low power factor wastes capacity and can incur utility penalties, and this calculator sizes the capacitor needed to correct it. You enter the real power in kilowatts, the current power factor, and the target power factor, and it returns the capacitor size in kVAR along with the current and target reactive power. Power factor is the ratio of real power (doing work) to apparent power (total supplied), and inductive loads like motors and transformers draw reactive power that lowers it. Correcting the power factor means adding capacitors that supply reactive power locally, reducing what the system must draw from the grid. The required capacitor kVAR is the real power times the difference between the tangents of the phase angles corresponding to the current and target power factors. Improving power factor has real benefits: it reduces the current drawn for the same real power, freeing up capacity in transformers and cables, cutting resistive losses, and avoiding the power factor penalties many utilities charge industrial customers with poor power factor. A common target is around 0.95, close enough to unity to capture most benefits without over-correcting. This calculation is essential for industrial electrical engineers designing capacitor banks. Note that over-correction (raising power factor above the target toward a leading power factor) can cause its own problems, so sizing to the target is important. Enter the real power and the current and target power factors to find the capacitor kVAR.
kVAR = P × (tan(arccos PF₁) − tan(arccos PF₂))
Power factor correction adds capacitors to supply reactive power that would otherwise be drawn from the grid. The required capacitor kVAR equals the real power times the difference between the tangent of the angle for the current power factor and the tangent for the target power factor.
Source:Electrical engineering
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter real power, current power factor and target power factor.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Capacitor size needed updates instantly as you type — no button to press.
Frequently asked questions
What is power factor correction?
Power factor correction adds capacitors to an electrical system to supply the reactive power that inductive loads like motors demand, reducing the reactive power drawn from the grid. This raises the power factor toward one, lowering the current needed for the same real power and improving efficiency, capacity, and often utility costs.
How do you size the correction capacitor?
The required capacitor kVAR equals the real power in kilowatts times the difference between the tangent of the arccosine of the current power factor and the tangent of the arccosine of the target power factor. The calculator performs this trigonometry from your inputs, giving the capacitor size needed to reach the target power factor.
Why is a low power factor a problem?
A low power factor means a large reactive component, so the system draws more current for the same real power. This overloads transformers and cables, increases resistive losses, reduces available capacity, and often triggers utility penalties for industrial customers. Correcting it reduces current, frees capacity, cuts losses, and can lower electricity bills.
What target power factor should I use?
A common target is around 0.95, which captures most of the benefits of correction while leaving a margin to avoid over-correction. Some utilities require a minimum power factor, often 0.9 or higher, to avoid penalties. Correcting all the way to exactly 1.0 is usually unnecessary and risks leading power factor issues, so a target near 0.95 is typical.
Can you over-correct the power factor?
Yes. Adding too much capacitance pushes the power factor past unity into a leading condition, where the system now has excess capacitive reactive power. This can cause voltage rise, resonance, and its own inefficiencies. Sizing the capacitor to reach the target power factor, rather than overshooting, avoids these problems, which is why accurate sizing matters.