Motor Power Calculator

Motor power can mean mechanical shaft output or electrical input. Mechanical output is related to torque and angular speed, while electrical input depends on voltage, current, phase configuration, and power factor. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

Choose the relationship that matches the data you actually know. Torque and RPM give mechanical power directly, while electrical measurements give input power that must be adjusted by efficiency to estimate shaft output. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

Convert torque to N·m, compute angular speed as 2π × RPM / 60, then multiply torque by angular speed. The result is mechanical power in watts and can be converted to kW or horsepower. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

The mechanical relationship is P = Tω. For rotating machines with speed in RPM, the equivalent equation is P = 2πNT/60 when T is in N·m and P is in watts. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

Convert kilowatts to watts and divide by 745.699871582 for mechanical horsepower. The result is a unit conversion only and does not automatically represent a motor's shaft rating unless the power basis is mechanical output. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

One kilowatt is approximately 1.34102 mechanical horsepower. The exact value depends on the horsepower definition, so this calculator distinguishes mechanical horsepower from metric horsepower and does not use boiler horsepower. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

One mechanical horsepower is approximately 0.745700 kW. NIST lists horsepower based on 550 ft·lbf/s at about 745.6999 W, which is the basis used for the mechanical-horsepower conversion here. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

Use T = P/ω. With power in watts and speed in RPM, T = P × 60 / (2π × RPM). The calculator also reports the equivalent torque in lb-ft and lb-in. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

Use P = Tω after converting torque to N·m and speed to radians per second. In imperial form, mechanical horsepower can also be approximated from torque in lb-ft times RPM divided by about 5252. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

Yes. At constant torque, mechanical power is proportional to rotational speed because P = Tω. If speed changes while torque also changes, the resulting power depends on both quantities, not RPM alone. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

Not necessarily. Higher RPM increases power only if torque is maintained. Real motors have torque-speed characteristics, current limits, voltage limits, field-weakening regions, and thermal constraints that can change torque as speed rises. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

Electrical input power enters the motor from the supply, while mechanical output power leaves through the shaft. Their difference represents motor losses, and efficiency relates them through η = Pout/Pin. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

For a fixed electrical input, higher efficiency means a larger fraction becomes useful mechanical output and less becomes loss. Efficiency is not the same as power factor, and both can vary with operating load. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

Motor efficiency is mechanical output power divided by electrical input real power. Multiply the ratio by 100 for percent. Reliable efficiency calculations require both powers to represent the same operating point and measurement conditions. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

For a balanced three-phase motor using line-to-line RMS voltage, electrical real input is Pin = √3 × V × I × PF. Multiply by motor efficiency to estimate mechanical output. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

The balanced line-based formula is Pin = √3VI PF, where V is line-to-line RMS voltage, I is line current, and PF is power factor. This is electrical input real power, not shaft output. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

For a single-phase motor, electrical real input is Pin = V × I × PF using RMS voltage and current. Mechanical output is then estimated as Pout = Pin × η when efficiency is known. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

Single-phase input uses VI PF, while balanced three-phase line-to-line input uses √3VI PF. The same motor output can therefore correspond to different current depending on supply phase, voltage, efficiency, and power factor. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

The √3 factor comes from the 120-degree phase relationship between line and phase quantities in a balanced three-phase system. It is used with line-to-line voltage and line current. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

If motor output power is known, first divide by efficiency to obtain electrical real input. Then divide by VPF for single phase or √3VPF for balanced three phase to obtain current. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

Yes. For fixed real power and voltage, a lower power factor requires more current because current is inversely proportional to PF in the simplified motor-current equations used by this calculator. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

Use measured data, the motor nameplate, manufacturer curves, or a justified design assumption for the actual operating point. Motor power factor can change substantially with load and motor design. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

Yes. Voltage, current, phase, and power factor determine electrical real input. Efficiency is then needed if you want to estimate mechanical shaft output from that electrical input. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

You can calculate electrical input power from voltage, current, and power factor without knowing efficiency. However, estimating mechanical shaft output from electrical input requires an efficiency value or a direct mechanical measurement. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

Yes. Torque and RPM determine mechanical power, which can be converted to mechanical horsepower. The calculation does not require electrical voltage or current because it is entirely on the mechanical side of the motor. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

A unique torque value requires motor speed. Convert 10 mechanical hp to watts, then apply T = P × 60 /(2πRPM). The torque changes inversely with speed for a fixed mechanical power. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

A unique torque value requires RPM. For 15 kW mechanical output, use T = 15000 × 60 /(2πRPM). A 15 kW motor therefore does not have one universal torque at every speed. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

Divide actual mechanical output by rated mechanical output and multiply by 100. Load factor is an operating ratio, not efficiency, and a lightly loaded motor may have different efficiency and power factor than at full load. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

Rated motor power is the manufacturer's stated output rating under defined operating conditions. It is commonly a mechanical output rating and should be read together with voltage, frequency, speed, duty, and other nameplate information. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

No. Rated power is a reference capability under specified conditions, while actual shaft power varies with load. Electrical input is larger than mechanical output whenever the motor has losses. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

Typical nameplate data can include rated power, voltage, current, frequency, speed, phase, power factor, efficiency, service factor, frame information, insulation class, enclosure, and NEMA or IEC design information. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

Motor losses do not remain constant with load. Copper loss, iron loss, friction, windage, stray load loss, and control losses contribute differently as the operating point changes. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

Yes. For a fixed mechanical power, torque decreases as speed increases because T = P/ω. For a real motor, available torque is governed by its torque-speed curve and control method. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

Voltage affects current, magnetic flux, torque capability, losses, and operating performance. The simplified input-power equations calculate a specified operating point but do not replace manufacturer limits or motor performance curves. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

Frequency influences synchronous speed and therefore the normal operating-speed range of AC motors. Actual shaft speed also depends on pole count, slip, load, and control method such as a variable-frequency drive. Use values from the actual operating point whenever possible because motor efficiency, power factor, torque, and current can change with load, speed, voltage, and control method.

Mechanical horsepower is based on approximately 745.6999 W per hp, while metric horsepower is approximately 735.49875 W per metric hp. They are close but not identical definitions. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

Approximately. One mechanical horsepower is about 745.6999 W, so 746 W is a common rounded engineering value. Use the more precise factor when accurate unit conversion is important. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.

There is no single standard efficiency percentage for every motor. Efficiency varies with motor type, size, pole count, load, enclosure, voltage, frequency, design, manufacturing date, and applicable regulatory category. For compliance or equipment decisions, verify the exact motor classification, manufacturing date, nameplate data, and the currently applicable regulation rather than applying one efficiency value to every motor.

No. Federal requirements apply by motor category and rating, and many motors may have different efficiency tables or may fall outside a particular covered scope. Nameplate and classification data are essential. For compliance or equipment decisions, verify the exact motor classification, manufacturing date, nameplate data, and the currently applicable regulation rather than applying one efficiency value to every motor.

For 2026, covered U.S. motors should be checked against the applicable provisions of 10 CFR §431.25 and the motor's exact classification. There is no universal 2026 efficiency percentage. For compliance or equipment decisions, verify the exact motor classification, manufacturing date, nameplate data, and the currently applicable regulation rather than applying one efficiency value to every motor.

10 CFR §431.25 includes provisions beginning June 1, 2027 for certain motor categories and ratings. Those future requirements should not be presented as already effective for all motors during 2026. For compliance or equipment decisions, verify the exact motor classification, manufacturing date, nameplate data, and the currently applicable regulation rather than applying one efficiency value to every motor.

No. It estimates power, torque, current, efficiency relationships, and load factor. Motor sizing also requires duty cycle, starting requirements, thermal limits, overload capability, load torque, ambient conditions, and application-specific margins. Use manufacturer data and applicable electrical or mechanical standards when the result supports equipment selection, protection, wiring, or safety-critical decisions.

No. It can support preliminary calculations, but final motor selection requires manufacturer performance data, speed-torque characteristics, enclosure, duty, service factor, mounting, environment, controls, and applicable standards. Use manufacturer data and applicable electrical or mechanical standards when the result supports equipment selection, protection, wiring, or safety-critical decisions.

No. Breaker sizing depends on code rules, motor full-load current definitions, starting current, branch-circuit protection, short-circuit conditions, conductor protection, and the specific installation. Use manufacturer data and applicable electrical or mechanical standards when the result supports equipment selection, protection, wiring, or safety-critical decisions.

No. Cable sizing requires ampacity, installation method, insulation temperature, ambient correction, grouping, voltage drop, fault-current withstand, termination limits, and applicable electrical codes. Use manufacturer data and applicable electrical or mechanical standards when the result supports equipment selection, protection, wiring, or safety-critical decisions.

No. Overload protection depends on motor nameplate data, service factor, temperature rise, controller characteristics, code requirements, and the protection device being used. Use manufacturer data and applicable electrical or mechanical standards when the result supports equipment selection, protection, wiring, or safety-critical decisions.

No. Starting current depends on motor design, locked-rotor code, supply impedance, starter or VFD method, load inertia, voltage, and control strategy. The steady-state equations on this page do not model acceleration. Use manufacturer data and applicable electrical or mechanical standards when the result supports equipment selection, protection, wiring, or safety-critical decisions.

No. Locked-rotor current is an equipment characteristic tied to motor design and test data. It should be obtained from the nameplate, manufacturer documentation, or applicable motor standards rather than estimated from normal running equations. Use manufacturer data and applicable electrical or mechanical standards when the result supports equipment selection, protection, wiring, or safety-critical decisions.

Not directly. A VFD system includes drive efficiency, harmonics, switching, DC-bus behavior, motor efficiency, control method, and loading. This calculator can estimate motor-side steady-state power relationships but is not a VFD input-power model. Use manufacturer data and applicable electrical or mechanical standards when the result supports equipment selection, protection, wiring, or safety-critical decisions.

Nameplate current is normally associated with rated conditions, while your calculation may use a different load, voltage, power factor, efficiency, or phase assumption. Motor current also varies with operating point and supply conditions. The calculator keeps mechanical and electrical power bases separate so the result is not mislabeled as rated horsepower, shaft power, or electrical input without the required assumptions.