Power Factor Correction (kVAr) Calculator
. Free, runs in your browser.
Your capacitor vendor says add more. Your bill says something else. Size the correction from your own numbers and see what poor power factor quietly bills you every month.
Runs entirely in your browser. Nothing you type is uploaded or stored.
The formula we use
kVAr needed = kW × (tan(acos(PF present)) − tan(acos(PF target)))
Extra billed units on kVAh billing = monthly kWh × (1 ÷ PF present − 1 ÷ PF target)
Monthly cost = extra units × energy rate
- Assumes a steady average load; real sites swing, which is why APFC panels switch in stages.
- On kW-billed connections the penalty is an explicit bill row instead; check your bill's PF clause.
- Harmonics-rich sites may need detuned reactors; a capacitor-only fix can make harmonics worse.
Typical numbers
Reference figures to sanity-check your inputs. Your own bill and equipment data always win.
At 0.90 average PF, a kVAh-billed consumer buys 11.1% more apparent-energy units than the same kWh load at unity PF.
Source: Power-triangle identity
A bill that shows both kWh and kVAh lets you derive the real average PF as kWh divided by kVAh.
Source: Power-triangle identity
Correcting a 100 kW load from 0.80 PF to 0.99 PF needs about 60.8 kVAr of capacitors before site derating.
Source: Power-triangle identity
IEEE 519 uses a 5% voltage-THD planning limit for systems at or below 69 kV, so detuned APFC should be checked when measured THDv reaches 5%.
Source: IEEE 519
Common questions
How much kVAr do I need to correct my power factor?
The kVAr needed equals load kW multiplied by the difference of the tangents of the phase angles at the present and target power factor: kVAr = kW x (tan(acos(PF1)) - tan(acos(PF2))). This calculator does that arithmetic; an APFC vendor should still stage it against your real load swings.
My bill prints PF 1.00. Why would I still need correction?
On kVAh billing the printed PF is close to 1.00 by construction. Divide kWh by kVAh on the same bill to get the derived PF; if that ratio is below 1, reactive power is being billed inside your units every month.
Can adding capacitors ever increase my bill?
Yes. An over-corrected or leading power factor has its own costs and risks. If your site swings between light and full load, a fixed bank overshoots at light load; automatic (APFC) switching sized in stages is the usual fix.