HP to kW Calculator
1 mechanical horsepower (HP) equals 0.7456999 kilowatts (kW) per NIST Special Publication 811, the authoritative US reference for SI conversion factors. Horsepower was created by...
Formula
Source: NIST SP 811, NEMA MG 1, IEC 60072 | Last reviewed: July 26, 2026
Examples
1 hp
= 0.7457 kW
1 HP = 0.746 kW -- base conversion
100 hp
= 74.57 kW
100 HP = 74.57 kW -- typical large industrial motor
0.5 hp
= 0.373 kW
1/2 HP = 0.373 kW -- fractional horsepower motor
250 hp
= 186.4 kW
250 HP = 186.4 kW -- heavy industrial drive
Quick Reference Table
| HP (NEMA) | kW (Exact) | Nearest IEC Frame |
|---|---|---|
| 0.5 | 0.373 | 0.37 kW |
| 1 | 0.746 | 0.75 kW |
| 2 | 1.491 | 1.5 kW |
| 3 | 2.237 | 2.2 kW |
| 5 | 3.728 | 4 kW |
| 7.5 | 5.593 | 5.5 kW |
| 10 | 7.457 | 7.5 kW |
| 15 | 11.19 | 11 kW |
| 20 | 14.91 | 15 kW |
| 25 | 18.64 | 18.5 kW |
| 30 | 22.37 | 22 kW |
| 40 | 29.83 | 30 kW |
| 50 | 37.28 | 37 kW |
| 60 | 44.74 | 45 kW |
| 75 | 55.93 | 55 kW |
| 100 | 74.57 | 75 kW |
| 125 | 93.21 | 90 kW |
| 150 | 111.9 | 110 kW |
| 200 | 149.1 | 150 kW |
| 250 | 186.4 | 200 kW |
| 300 | 223.7 | 220 kW |
| 400 | 298.3 | 315 kW |
| 500 | 372.8 | 375 kW |
| HP | kW |
|---|---|
| 0.25 | 0.186 |
| 0.5 | 0.373 |
| 1 | 0.746 |
| 2 | 1.49 |
| 3 | 2.24 |
| 5 | 3.73 |
| 7.5 | 5.59 |
| 10 | 7.46 |
| 15 | 11.2 |
| 20 | 14.9 |
| 25 | 18.6 |
| 50 | 37.3 |
| 75 | 55.9 |
| 100 | 74.6 |
| 200 | 149.1 |
| 500 | 372.8 |
| 1000 | 745.7 |
Popular Conversions
Quick answers for the most-searched hp to kW values.
100 HP to kW
100 hp = 74.57 kW
100 HP = 74.57 kW. The most-searched large motor conversion. A NEMA 100 HP motor is equivalent to an IEC 75 kW frame. At 480V 3-phase, 100 HP draws 124 FLA per NEC Article 430.
1 HP to kW
1 hp = 0.7457 kW
1 HP = 0.746 kW. Base conversion for all HP values. A 1 HP motor maps to a 0.75 kW IEC frame. Used for small pumps, fans, and compressor comparisons.
75 HP to kW
75 hp = 55.93 kW
75 HP = 55.93 kW. Common large industrial pump and compressor motor. Equivalent to IEC 55 kW. Installed in municipal water systems, HVAC chiller plants, and manufacturing lines.
10 HP to kW
10 hp = 7.457 kW
10 HP = 7.46 kW. Common commercial HVAC compressor and small industrial motor. Equivalent to IEC 7.5 kW frame. At 230V 3-phase, draws 28 FLA per NEC tables.
50 HP to kW
50 hp = 37.28 kW
50 HP = 37.3 kW. Standard industrial pump motor. Equivalent to IEC 37 kW. Used for irrigation pumps, process pumps, and hydraulic power units in manufacturing plants worldwide.
5 HP to kW
5 hp = 3.728 kW
5 HP = 3.73 kW. The largest single-phase motor commonly available. Equivalent to IEC 4 kW. Used for compressor duty, table saws, and small industrial fans. At 230V single-phase, draws 28 FLA.
Where is this used?
(1) Motor specification for export: a US pump manufacturer supplying a fire pump skid to a Saudi Arabian oil refinery must convert the 200 HP driver to 149 kW for IEC compliance documentation, equipment nameplates, and the customer's motor data sheets.
The conversion is also required for ATEX/IECEx hazardous area certification submissions, which use kW exclusively.
(2) Energy efficiency audits and utility incentives: a manufacturing plant with 15,000 HP of connected motor load needs to benchmark energy intensity (kWh/ton of product) against ISO 50001 targets.
Converting the motor inventory -- 15,000 HP x 0.7457 = 11,186 kW shaft aggregate -- provides the mechanical baseline.
With 88% average motor efficiency across the fleet, the estimated annual electrical consumption at 70% load factor is 11,186 x 0.70 / 0.88 x 8,760 = 78.0 GWh/yr.
This becomes the baseline for utility energy efficiency incentive applications, which require submission in kWh and kW, not HP.
(3) Backup generator sizing from motor load schedules: during design of an emergency power system for a hospital, the electrical engineer receives motor loads in HP from the mechanical engineer (chillers: 2 x 300 HP, pumps: 4 x 75 HP, fans: 10 x 25 HP).
Converting all to kW: chillers = 600 x 0.7457 = 447 kW shaft, pumps = 300 x 0.7457 = 224 kW, fans = 250 x 0.7457 = 186 kW, total shaft = 857 kW.
At 93% average efficiency: 857 / 0.93 = 921 kW electrical input.
With motor starting surge and NEC demand factors, a 1,500 kW diesel generator is selected.
(4) Variable frequency drive procurement: a 40 HP cooling tower fan needs a VFD.
ABB's catalog lists an ACS580-01-046A-4 drive rated at 30 kW heavy-duty.
40 HP x 0.7457 = 29.8 kW.
The 30 kW drive matches.
The engineer must not accidentally select the 22 kW (30 HP) drive by confusing kW and HP ratings on the catalog page.
(5) Marine and offshore classification: ABS, DNV, and Lloyds Register classification rules specify propulsion and auxiliary machinery power in kW.
A shipyard in Louisiana building a platform supply vessel with 2 x 2,000 HP main engines must convert to 2 x 1,491 kW for classification society plan approval.
(6) HVAC international procurement: a Canadian hospital evaluating chiller bids from a German manufacturer (quoted in kW compressor power) and a US manufacturer (quoted in compressor HP) converts the US unit's 350 HP compressor to 261 kW for direct kW/ton efficiency comparison against the German unit's 260 kW compressor at identical cooling capacity.
(7) Construction equipment specification: a North American contractor purchasing a European-manufactured tower crane with a 45 kW hoist motor needs to understand the hoist capacity in familiar HP terms for comparison against US-built cranes rated in HP.
45 kW = 60.4 HP.
(8) Power plant auxiliary systems: a US-based gas turbine power plant uses feedwater pumps rated in HP (1,200 HP boiler feed pump x 3 units).
The plant's heat rate calculation, required for EPA reporting, uses kW for all auxiliary loads.
Convert: 3,600 HP total x 0.7457 = 2,685 kW shaft auxiliaries, which at 94% efficiency consume 2,856 kW -- subtracted from the gross turbine output to calculate net station output and net heat rate in Btu/kWh.
Real-World Usage Scenarios
Fire pump export to a Middle Eastern hospital project
Ahmed, a mechanical engineer at a Houston-based pump manufacturer, is finalizing the documentation for a fire pump skid destined for a new hospital in Doha, Qatar. The pump is driven by a 150 HP NEMA Premium efficiency electric motor, UL listed and FM approved per NFPA 20. For the Qatari civil defense authority permit submission and the consulting engineer's review (Atkins, a UK-based firm using SI units exclusively), the motor rating must be expressed in kW. Ahmed converts: 150 HP x 0.7457 = 111.9 kW. He specifies a 110 kW motor in the export documentation -- the nearest standard IEC rating -- and verifies through the pump affinity curves that the 1.9 kW (1.7%) reduction does not compromise the certified fire flow performance at the required 150% duty point per NFPA 20. The IECEX certification body also requires the kW rating on the hazardous area compliance certificate. Without the conversion, the documentation package would be rejected by the authorities having jurisdiction, delaying the hospital's commissioning by months.
Manufacturing plant motor fleet energy baseline
Linda, an energy manager at an automotive parts plant in Ohio, is preparing documentation for the utility's industrial energy efficiency incentive program. The plant's motor inventory spreadsheet, maintained since 1995 by the maintenance department, lists 247 motors in HP only: 5 HP to 500 HP, totaling 18,450 HP of connected mechanical load. The utility requires submissions in kW and annual kWh. Linda's team converts the inventory: 18,450 HP x 0.7457 = 13,759 kW shaft capacity. Using logged production data, the average motor load factor is 62% and average nameplate efficiency is 89.5%. Estimated annual consumption: 13,759 x 0.62 / 0.895 x 8,760 = 83.4 GWh/yr. This becomes the pre-retrofit baseline. The team then models replacing the 100 largest motors (70% of total HP) with NEMA Super Premium (IE4) equivalents averaging 2.5% higher efficiency. Post-retrofit consumption drops to 81.1 GWh/yr -- a 2.3 GWh annual savings worth $184,000 at $0.08/kWh. The utility approves a $370,000 incentive based on the verified HP-to-kW conversion methodology. The entire financial case depends on correct HP-to-kW arithmetic across 247 data points.
Standby generator sizing for a water treatment plant expansion
Carlos, an electrical engineer at a design-build firm, is sizing the standby generator for a 40 MGD water treatment plant expansion. The mechanical engineer's load schedule lists seven critical pumps in HP: 2 x 300 HP (high-service pumps), 3 x 150 HP (backwash pumps), and 2 x 75 HP (chemical feed booster pumps). Carlos converts to shaft kW: 2 x 300 x 0.7457 = 447.4 kW; 3 x 150 x 0.7457 = 335.6 kW; 2 x 75 x 0.7457 = 111.9 kW. Total shaft power = 894.9 kW. He then applies 93% average motor efficiency for electrical input: 894.9 / 0.93 = 962.3 kW running load. The largest motor starting across-the-line (300 HP = 224 kW shaft) requires approximately 6x FLA inrush -- roughly 1,344 kVA for 10 seconds. Generator rule of thumb: engine kW must accommodate running load plus allow 30% voltage dip during largest motor start. Sizing calculation: 962 kW running + (300 HP x 0.746 / 0.93 x 3.5 starting kW factor) = 962 + 841 = 1,803 kW starting demand. Carlos specifies a 2,000 kW prime-rated diesel generator (Caterpillar 3516C). The HP-to-kW conversion was the foundational step -- without it, the entire sizing calculation would have been invalid, potentially resulting in a generator too small to start the largest pump motor during a power outage.
Common Mistakes to Avoid
Using electrical HP (746 W) vs mechanical HP (745.7 W)
Some vintage electrical engineering references and older textbooks use exactly 746 W = 1 HP as a convenient simplification. The difference is only 0.04% (746 vs 745.7), but it compounds across large motor inventories. For a plant with 20,000 HP of connected load, the error is 20,000 x (746 - 745.6999) = 6 kW -- roughly the power draw of a large residential air conditioner. While negligible for most industrial applications, this 6 kW error propagates into energy audit calculations, utility incentive applications, and greenhouse gas reporting (6 kW x 8,760 hr/yr = 52,560 kWh/yr x 0.4 kg CO2/kWh = 21 metric tons of phantom CO2). For precision energy metering, M&V protocols (IPMVP), and ESCO performance contracts with guaranteed savings, always use the NIST SP 811 value of 745.6999 W/HP. This calculator uses the precise mechanical horsepower value.
Forgetting that HP nameplate is shaft output, not electrical input
The most expensive conversion error in practice: a facilities engineer converts a 200 HP motor to 149.1 kW using this tool, then sizes the electrical panel, breaker, and feeder at 150 kW. The motor at 93% efficiency actually draws 200 x 0.7457 / 0.93 = 160.4 kW -- 10.3 kW (7%) more than the installed infrastructure rating. When the motor runs at full load during peak production, the 150 kW-rated feeder and breaker overheat and trip, stopping the production line. The cost: emergency electrician callout ($2,500), production downtime (4 hours x $50,000/hr = $200,000), and a rush-order new feeder and breaker ($15,000). The root cause: the 200 HP (149.1 kW) is shaft output. Electrical input is always shaft output divided by motor efficiency, which at 93% for a premium efficiency motor adds 7.5% more kW to the electrical demand. This calculator provides shaft power in kW -- the first step. For electrical infrastructure sizing, step two is dividing by motor efficiency and then using NEC Table 430.250 full-load amps.
Converting PS (metric horsepower) automotive ratings as if mechanical HP
European, Japanese, and Korean automotive manufacturers almost universally quote engine power in PS (Pferdestarke, DIN 66036), not mechanical HP. 1 PS = 735.4988 W = 0.9863 mechanical HP. A BMW 330i advertised at '258 PS' converts to 254 mechanical HP, not 258 HP. The 4 HP difference may seem trivial, but in the automotive world where marketing battles are fought over single-digit horsepower advantages, it matters. When an automotive journalist or importer converts PS to kW using the mechanical HP factor (0.7457) instead of the PS factor (0.7355), the kW value is off by 1.4%. For a 500 PS supercar, that is a 7 HP discrepancy in North American marketing materials. The correct chain: PS / 1.35962 = kW, or PS x 0.7355 = kW. The mechanical HP conversion (HP x 0.7457 = kW) is for industrial electric motors and SAE engine ratings only.
Industry Standards Referenced
Frequently Asked Questions
What is the formula to convert HP to kW?
kW = HP x 0.7456999. This is the exact mechanical horsepower conversion per NIST SP 811. For quick mental approximation: multiply HP by 3/4 (0.75). So 100 HP x 0.75 = 75 kW (close to exact 74.57 kW -- within 0.6%). For field estimates this shortcut works well because 0.7457 is effectively 3/4. The derivation from first principles: 1 HP = 33,000 ft-lbf/min. In SI units, 1 ft = 0.3048 m, 1 lbf = 4.44822 N. So 1 HP = 33,000 x 0.3048 x 4.44822 / 60 = 745.7 N-m/s = 745.7 W = 0.7457 kW. The 0.7456999 value with seven significant figures is the accepted engineering standard.
How many kW is 1 HP?
1 HP = 0.7457 kW. A 1 HP motor produces 0.746 kW of mechanical shaft power. The closest equivalent IEC motor size is 0.75 kW -- slightly more powerful than a 1 HP motor (0.75 kW = 1.006 HP). When replacing a 1 HP NEMA motor with an IEC motor, the 0.75 kW size is the correct substitution -- the 0.006 HP (0.6%) difference is within manufacturing tolerance and motor service factor. For precision applications like dynamometers or test stands, use the exact conversion and specify the required shaft power in kW rather than the approximate frame size.
How many kW is 75 HP?
75 HP = 55.93 kW. This is a very common industrial motor size -- a 75 HP motor maps to a 55 kW IEC frame. These motors are used extensively for large irrigation pumps, industrial air compressors (75 HP rotary screw compressors deliver approximately 350 CFM at 125 PSI), cooling tower fans, and process water pumps in chemical plants and refineries. At 480V 3-phase, a 75 HP motor draws 96 FLA per NEC Table 430.250. The 55 kW IEC equivalent at 400V 50Hz draws approximately 99 A.
Are there different types of horsepower?
Yes. Mechanical (imperial) horsepower = 745.6999 W -- used for electric motors in North America per NEMA MG 1 and for engine ratings per SAE J1349. Metric horsepower (PS, CV, DIN) = 735.4988 W -- used in continental Europe for automotive and some industrial applications; 100 PS = 98.6 mechanical HP. Boiler horsepower (BHP) = 9,809.5 W -- defined as the heat required to evaporate 34.5 lb/hr of water at 212F; used only in the US steam boiler industry per ASME BPVC. Electric horsepower = exactly 746 W -- a simplified convention sometimes used in older textbooks and basic electrical calculations. Hydraulic horsepower = (Flow in GPM x Pressure in PSI) / 1714 -- the fluid power delivered by a pump, before pump efficiency losses. Brake horsepower (BHP) in engine contexts refers to the net output measured at the flywheel with a dynamometer (brake), as distinct from indicated horsepower inside the cylinders. This calculator uses mechanical horsepower (745.6999 W) unless the user specifies otherwise.
Can I use this to calculate the kW input to my motor?
No. This calculator converts the mechanical HP rating (shaft output) to mechanical kW. To calculate the electrical kW input, you must divide by motor efficiency: Electrical kW input = (HP x 0.7457) / Efficiency. For example, a 100 HP motor with 93% efficiency draws (100 x 0.7457) / 0.93 = 80.2 kW of electricity -- not 74.6 kW. The 5.6 kW difference is lost as heat in the stator windings (I^2R losses), rotor, friction, windage, and core losses per IEEE 112 test method B. Always refer to the motor nameplate for full-load amps (FLA) and nominal efficiency when performing electrical system design. The NEC requires using FLA from Table 430.250 (not nameplate HP converted to kW) for conductor and overcurrent protection sizing.
Why do IEC motor kW ratings not match exact HP conversions?
IEC motor kW ratings follow standard Renard R20/R40 preferred number series per IEC 60072: 0.37, 0.55, 0.75, 1.1, 1.5, 2.2, 3, 4, 5.5, 7.5, 11, 15, 18.5, 22, 30, 37, 45, 55, 75, 90, 110, 132, 160, 200 kW. These are geometric progressions chosen for manufacturing economy -- each step is approximately 1.12-1.25x the previous. NEMA HP ratings follow their own commercial tradition: 1/4, 1/3, 1/2, 3/4, 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150, 200, 250, 300, 400, 500 HP. The match is approximate. When substituting, verify the actual shaft power (not just nominal rating), frame size mechanical compatibility (IEC 56-450 vs NEMA 42-680), mounting dimensions (foot, flange, face), shaft diameter and keyway, and electrical characteristics (voltage, frequency, insulation class).
Reviewed for accuracy
Reviewed against NIST SP 811 mechanical horsepower definition, NEMA MG 1 motor nameplate standards, and IEC 60072 standard motor output ratings · Last reviewed: July 26, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.