SizingKitMotor nameplates
kW to Amps Calculator
A kilowatt plate on a motor is shaft output, so the current is the rating divided by the efficiency, then by the power factor, then by the voltage and 1.732 if it is three-phase — this free calculator keeps those two terms apart instead of merging them, and needs no signup. It also prints the NEC Table 430.250 value beside your figure, because the code sizes conductors on the table and overloads on the plate, and the two are not the same number.
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- No signup
- NEC 430.248 and 430.250
- Efficiency term separate
- Blank cells stay blank
Kilowatts unless you name another unit. The table is indexed in horsepower, and this works out at 10.06 hp.
These are the table’s own columns, and they are rated motor voltages rather than system voltages: the 460 V column is what a 480 V system uses, the 230 V column what a 240 V system uses.
Default 1.00 — No efficiency applied. The page starts by treating the figure you typed as electrical input power, which is what it is on a resistance heater, a rectifier or a plate marked kW input, and leaves the term at one until you tell it otherwise. A motor plate in kilowatts is shaft output, and NEMA MG 1 and IEC 60034-1 both require the full-load efficiency to be marked on it. Read that figure off the plate — general-purpose induction motors run roughly 82% at 1 kW and 95% at 100 kW, and the spread across that range is far too wide for this page to pick one for you.
Default 0.80 — A holding figure only, sitting where the plate's own cos φ belongs. IEC 60034-1 and NEMA MG 1 both require a polyphase induction motor to carry its rated power factor on the nameplate, so on this page the number is always available to be read rather than assumed. Power factor tracks load rather than machine: a motor marked 0.86 at full load falls into the 0.5s at a quarter torque, because the magnetizing current is nearly constant while the torque-producing current is not. Where a variable-frequency drive stands between the line and the motor, the figure that matters at the panel is the drive's input displacement power factor, and the motor's marked figure describes only what happens downstream of it.
Computed from the plate
11.8 A
Sizes the running overload, and nothing else — NEC 430.32.
Code table value
—
Sizes the conductor, the disconnect and the short-circuit device — NEC 430.6(A)(1).
| Rating in kilowatts and horsepower | 7.5 kW · 10.1 hp |
|---|---|
| Electrical input after efficiency | 7.5 kW |
| Apparent power the supply sees | 9.37 kVA |
| Branch-circuit conductor minimum, 125% of the table | — |
| Overload device maximum, 1.25× the plate | 14.7 A |
| Where this current sits against the table value | — |
| Efficiency × power factor the table row implies | — |
10.06 hp is not a row of this table, and the table is entered by the motor’s horsepower rating rather than by arithmetic on its kilowatts. The neighboring rows are 10 hp and 15 hp — 14 A and 21 A in this voltage column. Take the rating the manufacturer assigned the machine and read that row; a motor plated at 7.5 kW is sold as 10 hp, not as 10.06 hp.
These are the code's table values, not the motor's nameplate current, and the two are different on purpose. NEC 430.6(A)(1) requires the values in Tables 430.247 through 430.250 to be used — instead of the nameplate — whenever sizing conductors, ampacity, switches and branch-circuit short-circuit and ground-fault protection. The nameplate governs exactly one thing: the running overload device, under 430.6(A)(2) and 430.32. The table figures are deliberately conservative and run above what a modern high-efficiency motor actually draws, so substituting a lower nameplate current under-sizes the conductor and the disconnect. The two exceptions are a listed motor-operated appliance and a multispeed motor, which use their nameplate for both.
Kilowatts, horsepower and table full-load amperes at 460 V
Table 430.250, 460 V column, with the kilowatt equivalent of each horsepower row computed at 0.7457 kW per hp. An empty cell is a cell this site does not carry.
| hp | kW | Table FLA | 125% conductor |
|---|---|---|---|
| 1/2 | 0.37 | 1.1 | 1.4 |
| 3/4 | 0.56 | 1.6 | 2 |
| 1 | 0.75 | 2.1 | 2.6 |
| 1-1/2 | 1.12 | 3 | 3.8 |
| 2 | 1.49 | 3.4 | 4.3 |
| 3 | 2.24 | 4.8 | 6 |
| 5 | 3.73 | 7.6 | 9.5 |
| 7-1/2 | 5.59 | 11 | 13.8 |
| 10 | 7.46 | 14 | 17.5 |
| 15 | 11.19 | 21 | 26.3 |
| 20 | 14.91 | 27 | 33.8 |
| 25 | 18.64 | 34 | 42.5 |
| 30 | 22.37 | 40 | 50 |
| 40 | 29.83 | 52 | 65 |
| 50 | 37.29 | 65 | 81.3 |
| 60 | 44.74 | 77 | 96.3 |
| 75 | 55.93 | 96 | 120 |
| 100 | 74.57 | 124 | 155 |
| 125 | 93.21 | 156 | 195 |
| 150 | 111.86 | 180 | 225 |
| 200 | 149.14 | 240 | 300 |
| 250 | 186.43 | 302 | 377.5 |
| 300 | 223.71 | 361 | 451.3 |
| 350 | 261 | 414 | 517.5 |
| 400 | 298.28 | 477 | 596.3 |
| 450 | 335.57 | 515 | 643.8 |
| 500 | 372.85 | 590 | 737.5 |
NEC (NFPA 70) 2023, Table 430.250 — Full-Load Current, Three-Phase Alternating-Current Motors, the induction-type squirrel cage and wound-rotor columns. Voltages are 115, 200, 208, 230, 460 and 575.
How to get amps out of a kilowatt motor plate
The order of the two divisions matters, and the table lookup answers a different question than the arithmetic does.
Type the rating and unwind the efficiency first
The kilowatts stamped on an induction motor are the mechanical output at the shaft, so the electricity going in is that figure divided by the full-load efficiency the plate also carries. Leave the efficiency at 1.00 only when the rating you have is already electrical input — a resistance bank, a rectifier, a plate explicitly marked kW input.
Apply the plate's own cos φ, not a rule of thumb
Power factor turns input watts into the volt-amperes the supply actually delivers, and IEC 60034-1 requires the figure to be marked, so it is available to be read rather than assumed. Enter it and the arithmetic current updates; the field starts at 0.80 purely so the form has something in it.
Compare your figure against the table row and use each for its own purpose
Pick the rated motor voltage from the list — those are the columns the code table actually has — and the page returns the table's full-load amperes next to your calculated ones. Size conductors, the disconnect and the short-circuit device on the table current under 430.6(A)(1); size the running overload on your calculated plate current under 430.32. Switch the first field to a clamp reading and the whole chain runs the other way, ending at the kilowatts the machine is delivering right now.
Tables read, rules applied and figures assumed
| Single-phase table | NEC Table 430.248, twelve horsepower rows from 1/6 to 10 hp, across the 115, 200, 208 and 230 V columns. |
|---|---|
| Three-phase table | NEC Table 430.250, twenty-seven rows from 1/2 to 500 hp, across 115, 200, 208, 230, 460 and 575 V. |
| Cells returned empty on purpose | 40 hp and 350 hp at 575 V. Both recalled values contradict the 0.8 ratio the rest of that column obeys, so the page prints nothing and sends you to the code book. |
| Rating conversion | 1 hp = 0.7457 kW, derived from 550 ft·lbf/s. A 7.5 kW motor is 10.06 hp and is sold as a 10 hp machine, which is the row to read. |
| Conductor rule applied | NEC 430.22(A), 125% of the table current: 10 hp at 460 V is 14 A on the table, so the branch-circuit conductors need 17.5 A of ampacity. |
| Overload rule applied | NEC 430.32(A)(1), 125% of nameplate current where the service factor is 1.15 or more or the marked rise is 40 °C, and 115% for everything else. |
| What the code table itself assumes | Divide a row's shaft output by the volt-amperes it implies and the 10 hp, 460 V cell returns 0.669 for efficiency times power factor — deliberately below what an IE3 machine achieves. |
| Reverse direction | A clamp reading on one line conductor runs the same chain backwards to input kilowatts and shaft output, and reports the reading as a percentage of the table full-load current. |
| Efficiency default | 1.00, meaning no efficiency term has been applied yet, editable in place and marked as the assumption it is. |
| Where it runs | In this tab only. Plate readings you type are never transmitted or stored. |
Frequently asked questions
My motor plate says 7.5 kW. Is that what it pulls from the line?
No — it is what the shaft delivers, and the line has to supply more. At 91 percent efficiency that 7.5 kW of mechanical output needs 8.24 kW of electrical input, and at 0.86 power factor the supply is handing over 9.58 kVA to deliver it. Only the last of those three numbers has anything to do with how big the wire is.
Which current sizes the wire: the one I calculated or the table's?
The table's, without exception, under NEC 430.6(A)(1). Conductors, ampacity, the disconnecting means and the branch-circuit short-circuit and ground-fault device are all sized on the value from Table 430.247 through 430.250, and substituting a lower plate current is how a feeder ends up a size light. The two documented exceptions are a listed motor-operated appliance and a multispeed motor, both of which use the plate for everything.
Why keep efficiency and power factor as separate terms?
Because they describe two unrelated losses and only one of them costs you energy. Efficiency is the share of input power that never reaches the shaft — it leaves as heat in the windings, the iron and the bearings — while power factor describes current that flows without doing net work at all, going out and coming back each half cycle to magnetize the iron. Multiplying them into one fudge factor works until you change the load, at which point efficiency barely moves and power factor collapses.
My motor is 400 V, 50 Hz. Which table column applies?
None of them — Tables 430.248 and 430.250 are written for 60 Hz North American systems and their columns are rated motor voltages used for 110–120, 220–240, 440–480 and 550–600 V systems. A 400 V IEC machine falls outside that entirely, so the arithmetic on this page is your figure and the table lookup is not applicable. The same machine on a 480 V system also turns at six-fifths of its plate speed and draws differently, which is a separate problem from this one.
Does a variable-frequency drive change what the panel sees?
Yes, and it moves the question upstream of the motor entirely. The drive's rectifier draws a distorted, non-sinusoidal current whose displacement power factor is typically high but whose total power factor is dragged down by harmonics, so the motor's marked cos φ describes only the drive output. Size the supply on the drive's own input current rating from its manual, and treat 430.6 as applying to the drive as the utilization equipment.
Why are the 40 hp and 350 hp cells blank at 575 V?
Because this site could not confirm those two figures to the standard it holds itself to, and a wrong full-load current sizes a conductor wrong. Every other cell in the 575 V column sits at 0.8 times the 460 V figure; the values recalled for those two do not, and the disagreement could not be resolved, so they are stored as nothing rather than as a plausible guess. Read them from the printed code book.
Is a kilowatt rating on a heater treated the same way?
No, and it is simpler: a resistance heater's kW rating is already electrical input, so leave the efficiency at 1.00 and the power factor at 1.00. Effectively all of the energy becomes heat inside the room being heated, which means the distinction between input and output that governs a motor does not exist here. Nothing in Article 430 applies to it either — a heater is not a motor load.
About kilowatt nameplates, NEC 430.6 and the two currents a motor has
Outside North America a motor is rated in kilowatts, and inside it a motor is rated in horsepower, but the interesting difference is not the unit — it is that both figures describe the output. A 7.5 kW motor and a 10 hp motor are within one percent of the same machine, and neither number tells you what the supply delivers until the efficiency and the power factor have been applied in that order. That is why a page that simply divides kilowatts by volts is not a motor tool at all; it is the watts to amps calculator with a prefix attached, and it belongs to a different question about a different kind of nameplate.
The rule that surprises people is that the code does not want your arithmetic. NEC 430.6(A)(1) directs that the values in Tables 430.247 through 430.250 be used for conductors, ampacity, switches and branch-circuit short-circuit protection — the table, not the plate, and not a measurement either. Those table figures were compiled against older, less efficient machines and run visibly high: read the 10 hp, 460 V row backwards and it implies a combined efficiency and power factor of 0.669, well under what a modern premium-efficiency motor achieves. The conservatism is deliberate, because a conductor has to serve whatever motor is bolted in next, not only the one there today. The nameplate then wins back exactly one decision: the running overload device under 430.32, which protects this motor and so is set from this motor’s marked current.
Two neighboring conversions are deliberately not folded in here. A transformer or a generator is rated in kVA rather than kW because it does not know what will be plugged into it, and that rating turns into current without any power factor at all — the kVA to amps calculator handles that, along with the primary and secondary amps of the same machine. And where the kilowatts you care about are being produced rather than consumed, torque and speed are the inputs, not volts and amps: the torque to horsepower calculator works from the shaft side, and the UPS runtime calculator from the battery side.
Where a plate reading goes when you type it here
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — loads, lengths, nameplate ratings, the rates your utility charges you — is uploaded, logged or kept, which is also why the calculators carry on working in a mechanical room with no signal.
The horsepower table, the 125 percent conductor rule and the overload multipliers are compiled into the page itself, so the lookup is a local array read and not a request to anything.