Amps to Kilowatts Calculator
32 amps. That's what the clamp meter shows, clipped around one conductor on a 208 V three-phase panel: a live, measured fact, not a nameplate figure. But amps alone don't say how much real power that circuit is delivering. Getting from that reading to kilowatts means folding in the voltage the panel is actually running and the power factor the connected load is actually pulling, since a resistive heater and an induction motor can draw the exact same current while doing very different amounts of real work.
Live, no submit
Real power
10.03kW
Formula, live
kW = (√3 × V × A × PF) / 1000
kW = (√3 × 208 × 32 × 0.87) / 1000 = 10.03 kW
Why a clamp-meter reading isn't kW yet
A clamp meter measures current magnitude. It has no way of knowing what fraction of that current is doing real work versus circulating back and forth without ever landing on the load. Multiplying the reading straight through by voltage gives apparent power, measured in kVA, and apparent power is always equal to or larger than real power. The gap between the two is power factor, and closing that gap is the whole point of the conversion below.
That's why the same 32 A reading can represent very different loads on two different panels. A resistive heater running near unity power factor turns almost all of that apparent power into real power. A panel feeding compressors and motors, running at a lower power factor, turns noticeably less of the same current into usable kilowatts. The clamp meter alone can't tell the two apart.
In practice, that means a facilities technician can't stop at the meter's display. A nameplate power factor, a spec sheet, or a dedicated power meter's own reading has to supply the missing piece before the amp figure on the clamp turns into a defensible kW number. Otherwise the only honest output of the reading is apparent power, not real power.
From clamp reading to kilowatts
Watt's Law starts the same way it does in reverse: P = V × I. For a three-phase line-to-line reading, that relationship gets one more term, because the three phases peak 120° apart and a line-to-line voltage already reflects a vector sum rather than a plain arithmetic one. The √3 multiplier accounts for that geometry, and the power factor scales the result down from apparent power to real power.
For a single-phase or DC reading, the √3 term simply drops out of the denominator, leaving kW = (V × A × PF) / 1000. DC circuits fix power factor at 1.0 since there's no phase angle to correct for. The calculator above switches formulas automatically based on the circuit type selected.
Worked example: reading the panel
32 A measured on one line, 208 V three-phase line-to-line, power factor 0.87 (motor-mixed load).
- 1
Apply the three-phase formula
kW = (√3 × 208 × 32 × 0.87) / 1000
- 2
Find the apparent power first
1.7321 × 208 × 32 = 11,528.5 (11.53 kVA)
- 3
Apply the power factor and scale to kilowatts
11,528.5 × 0.87 / 1000 = 10.03 kW
This is general reference arithmetic based on a single clamped reading, not a substitute for a proper load study. A licensed electrician or a dedicated power meter confirms real power on an actual panel.
What the clamp meter can and can't see
A clamp meter sits on the current path and reports one number: amps. It has no view of the voltage waveform's timing relative to that current, so it can't tell you, on its own, how much of the reading is real power and how much is reactive current riding along without ever reaching the load. The diagram below shows where each downstream number comes from once voltage and power factor are added back in.
Common clamp readings, amps to kW
Three-phase, 208 V line-to-line, power factor 0.87, typical of a commercial panel carrying a mix of motor and general loads. A different power factor or voltage shifts every value in this table.
| Amps | Real power at 208 V, PF 0.87 |
|---|---|
| 10 A | 3.13 kW |
| 20 A | 6.27 kW |
| 32 A | 10.03 kW |
| 40 A | 12.54 kW |
| 60 A | 18.81 kW |
| 80 A | 25.07 kW |
| 100 A | 31.34 kW |
| 150 A | 47.01 kW |
Reference estimates only, not measured values: confirm any real panel against its own clamp-meter reading, voltage and power factor.
Where a current reading goes next
Questions
Amps to kilowatts FAQ
Questions that come up once a clamp-meter reading has to turn into a real power figure.
Why does a clamp-meter reading need a power-factor correction before it becomes real kW?
A clamp meter measures the magnitude of current flowing in a conductor, but it has no way of knowing how much of that current is doing real work versus just circulating reactive energy. That split is what power factor describes. Multiplying volts by amps alone gives apparent power in kVA, not kW. For 32 A at 208 V three-phase, that apparent figure is 11.53 kVA; only after applying the 0.87 power factor does the real 10.03 kW appear. Skip the power factor and every clamp reading overstates the real power the circuit is delivering.
Do you clamp one conductor or all three on a three-phase panel?
For a quick check, technicians typically clamp one line conductor at a time, since a healthy balanced three-phase circuit should draw close to the same current on all three legs. A dedicated three-phase power meter instead uses three current transformers simultaneously, one per line, which is the only way to catch an unbalanced load or get a true combined power reading without assuming the phases match. A single clamp reading is a spot check, not a guarantee of balance.
What does it mean if the clamp meter reads current on the neutral conductor instead of a hot leg?
The amps value that belongs in the three-phase kW formula comes from clamping a hot conductor, not the neutral. Those are two different measurements with two different meanings. In a balanced wye system, the neutral carries only the residual current left over when the three phases don’t cancel out perfectly, so it should read low or near zero. A high neutral reading signals imbalance between the phases, not additional load current to fold into a power calculation.
Can two panels reading the same amps carry different real power?
Yes, current alone doesn’t determine real power, because power factor changes how much of that current is actually doing work. Two 208 V three-phase panels both clamped at 32 A can differ sharply in kW: a resistive heating load near PF 1.0 delivers about 11.53 kW, while a motor-heavy load at PF 0.7 delivers only about 8.07 kW at the same current. The amp reading is identical; the real power is not.
How accurate is a clamp meter compared with a dedicated power meter?
As general reference, a typical true-RMS clamp meter is commonly specified around ±1.5% to ±3% of reading for current, while a dedicated power meter or data logger is usually tighter because it measures voltage, current and phase angle together instead of estimating power from a separately assumed power factor. For a one-off spot check, a clamp meter reading is normally close enough to size or sanity-check a load. For billing-grade or load-study work, check the specific meter’s datasheet rather than assuming a figure, since accuracy varies by model and by how close the reading is to the meter’s rated range.
Why did my clamp meter read 208 V line-to-line instead of 240 V on this panel?
A reading of 208 V line-to-line usually means the panel is fed from a 120/208 V three-phase wye system, which is common in US commercial buildings because it supplies both 120 V single-phase branch circuits and 208 V three-phase equipment from one service. That 208 V figure isn’t a rounding of 240 V. It comes from 120 × √3 ≈ 207.85 V, the vector sum of two 120 V phases 120° apart. A panel built on a delta or split-phase system instead, more typical of lighter commercial or residential services, reads 240 V line-to-line.