VA = HP × 746 ÷ (η × PF) · HP = VA × η × PF ÷ 746📊 Quick Reference (η=85%, PF=0.85)
| HP | VA | kVA |
|---|---|---|
| 1 | 1,033 | 1.03 |
| 2 | 2,065 | 2.07 |
| 5 | 5,163 | 5.16 |
| 10 | 10,326 | 10.33 |
| 25 | 25,813 | 25.81 |
| 50 | 51,626 | 51.63 |
Converting HP to VA (horsepower to volt-amperes) is essential whenever you need to size a UPS, generator, transformer, or electrical panel for a motor load. HP is a unit of mechanical output power; VA is a unit of apparent electrical power—the product of voltage and current that the supply must deliver. Because every motor has losses (efficiency < 100 %) and draws reactive current (power factor < 1), the VA a motor demands is always higher than its HP rating converted directly to watts. The master formula is VA = HP × 746 ÷ (η × PF).
🔄 Need the reverse calculation? If you need to convert from VA to HP (the opposite direction of this page), use our dedicated VA to HP calculator with full conversion tables, step-by-step examples, and engineering formulas.
As a rough rule of thumb, 1 HP ≈ 1,000 VA for a typical motor with 85 % efficiency and 0.85 power factor. But the exact value can range from 800 VA to over 1,200 VA per HP depending on motor size and type. Use the calculator above for an instant answer, or keep reading for the complete formula derivation, tables for standard motor sizes, and six worked examples covering real-world UPS sizing, generator selection, and transformer loading.
HP to VA Conversion Table — Standard Motor Sizes
The table below shows the approximate VA demand for common motor HP ratings. The “typical” column uses representative efficiency and power factor values for each size per NEMA MG-1 data. The “η = 85 %, PF = 0.85” column uses uniform values for quick estimation.
| HP | Watts (HP × 746) | Typical η | Typical PF | VA (typical) | VA (η=85%, PF=0.85) |
|---|---|---|---|---|---|
| 0.5 | 373 | 0.72 | 0.63 | 823 | 517 |
| 1 | 746 | 0.82 | 0.75 | 1,213 | 1,033 |
| 1.5 | 1,119 | 0.84 | 0.78 | 1,708 | 1,549 |
| 2 | 1,492 | 0.84 | 0.80 | 2,220 | 2,065 |
| 3 | 2,238 | 0.86 | 0.82 | 3,173 | 3,098 |
| 5 | 3,730 | 0.88 | 0.84 | 5,046 | 5,163 |
| 7.5 | 5,595 | 0.90 | 0.86 | 7,229 | 7,745 |
| 10 | 7,460 | 0.91 | 0.86 | 9,532 | 10,326 |
| 15 | 11,190 | 0.92 | 0.87 | 13,981 | 15,490 |
| 20 | 14,920 | 0.92 | 0.87 | 18,641 | 20,653 |
| 25 | 18,650 | 0.93 | 0.88 | 22,788 | 25,813 |
| 50 | 37,300 | 0.93 | 0.89 | 45,065 | 51,626 |
| 75 | 55,950 | 0.94 | 0.89 | 66,878 | 77,447 |
| 100 | 74,600 | 0.95 | 0.90 | 87,252 | 103,261 |
Notice that larger motors have higher efficiency and power factor, which means their VA-per-HP ratio gets closer to 746. Small motors (0.5–2 HP) have notably worse efficiency and PF, making their VA demand per HP significantly higher. Always use actual nameplate data when available rather than these estimates.
HP to VA Formula — Step by Step
The conversion requires an intermediate step: HP is mechanical output power, which must first be converted to watts, then divided by efficiency to get electrical watts, and finally divided by power factor to get VA (apparent power).
The Master Formula
Where: HP = horsepower (mechanical output) · 746 = watts per HP · η = motor efficiency (decimal) · PF = power factor (decimal).
Step 1 — Convert HP to mechanical watts: W = HP × 746. For example, 5 HP = 5 × 746 = 3,730 W.
Step 2 — Divide by efficiency to get electrical watts: W_elec = 3,730 ÷ 0.85 = 4,388 W.
Step 3 — Divide by power factor to get VA: VA = 4,388 ÷ 0.85 = 5,163 VA.
Or in one step: VA = 5 × 746 ÷ (0.85 × 0.85) = 3,730 ÷ 0.7225 = 5,163 VA.
Inverse Formula — VA to HP
Example: A UPS rated 10,000 VA can supply HP = 10,000 × 0.85 × 0.85 ÷ 746 = 7,225 ÷ 746 = 9.69 HP of motor load (assuming η = 85 %, PF = 0.85).
Why Not Just Multiply by 746?
HP × 746 gives you the mechanical output in watts, but the electrical system must deliver more power than the shaft output for two reasons. First, some energy is lost as heat inside the motor (copper losses, iron losses, friction)—efficiency accounts for this. Second, the motor draws reactive current to magnetize its core—power factor accounts for this. Ignoring either one leads to undersized electrical equipment. For related power conversions, see our Amps to kW calculator.
1-Phase vs. 3-Phase — How Phase Count Affects the Calculation
The HP-to-VA formula does not change with the number of phases. Whether the motor is single-phase or three-phase, the apparent power it draws in VA is calculated the same way: VA = HP × 746 ÷ (η × PF). The phase count only matters when you need to find the current from the VA result.
| Parameter | 1-Phase | 3-Phase |
|---|---|---|
| HP to VA formula | VA = HP × 746 ÷ (η × PF) | VA = HP × 746 ÷ (η × PF) |
| Current from VA | I = VA ÷ V | I = VA ÷ (√3 × V_LL) |
| Typical voltage | 120 V or 230 V | 208 V, 230 V, 460 V |
| Example: 5 HP at 5,163 VA | I = 5,163 ÷ 230 = 22.4 A | I = 5,163 ÷ (1.732 × 460) = 6.48 A |
| Common sizes | Up to ~5 HP | 1 HP and up, any size |
| Typical PF range | 0.65–0.85 | 0.75–0.90 |
Single-phase motors generally have lower power factor than equivalent three-phase motors, meaning they demand more VA per HP. For current calculations on specific motor circuits, see our Amps to HP calculator and Amperes to VA calculator.
VA to HP — Inverse Conversion
Going from VA back to HP is useful when you know a UPS or generator’s VA rating and need to determine how many HP of motor load it can support.
| VA (or kVA) | HP (η=85%, PF=0.85) | HP (η=90%, PF=0.87) | Application |
|---|---|---|---|
| 1,000 VA | 0.97 | 1.05 | Small UPS, fractional-HP motor |
| 3,000 VA | 2.91 | 3.15 | Home standby generator |
| 5,000 VA | 4.84 | 5.25 | Workshop UPS or small genset |
| 10 kVA | 9.69 | 10.49 | Commercial UPS, panel transformer |
| 25 kVA | 24.22 | 26.23 | Industrial transformer secondary |
| 50 kVA | 48.44 | 52.46 | Large commercial generator |
| 100 kVA | 96.89 | 104.93 | Industrial generator, pad-mount transformer |
For UPS sizing with power-factor and headroom considerations, see our UPS Sizing Calculator.
6 Solved Examples — HP to VA in Real Scenarios
Example 1 — UPS Sizing for a 5 HP Motor (1-Phase, 230 V)
Data: HP = 5, η = 0.85, PF = 0.85
Formula: VA = HP × 746 ÷ (η × PF)
Calculation: VA = 5 × 746 ÷ (0.85 × 0.85) = 3,730 ÷ 0.7225 = 5,163 VA
You need a UPS rated at least 5.2 kVA for this motor. Adding 20 % margin for starting inrush, specify a 6 kVA or 7.5 kVA UPS. On 1-phase 230 V the running current is 5,163 ÷ 230 = 22.4 A.
Example 2 — Generator Load: 1 HP Compressor (1-Phase, 120 V)
Data: HP = 1, η = 0.82, PF = 0.75
Formula: VA = HP × 746 ÷ (η × PF)
Calculation: VA = 1 × 746 ÷ (0.82 × 0.75) = 746 ÷ 0.615 = 1,213 VA
A 1 HP single-phase compressor draws about 1.2 kVA running. Starting VA can be 3–6 times higher (3.6–7.3 kVA), so a portable generator should be rated at least 3.5 kW to handle the inrush. Running current: 1,213 ÷ 120 = 10.1 A.
Example 3 — Transformer Sizing: 10 HP Pump (3-Phase, 460 V)
Data: HP = 10, η = 0.91, PF = 0.86
Formula: VA = HP × 746 ÷ (η × PF)
Calculation: VA = 10 × 746 ÷ (0.91 × 0.86) = 7,460 ÷ 0.7826 = 9,532 VA
A 10 HP pump draws ~9.5 kVA. If this is the only load on a dry-type transformer, a 15 kVA transformer is the minimum standard size, leaving headroom for other branch circuits and starting transients. Line current: 9,532 ÷ (1.732 × 460) = 11.96 A.
Example 4 — 1.5 HP Air Handler (1-Phase, 230 V)
Data: HP = 1.5, η = 0.84, PF = 0.78
Formula: VA = HP × 746 ÷ (η × PF)
Calculation: VA = 1.5 × 746 ÷ (0.84 × 0.78) = 1,119 ÷ 0.6552 = 1,708 VA
A typical residential HVAC blower motor. The UPS or generator must supply at least 1.7 kVA running. For circuit sizing, the current is 1,708 ÷ 230 = 7.43 A on a 230 V single-phase supply.
Example 5 — High-Efficiency Motor: 25 HP (3-Phase, 460 V, IE3)
Data: HP = 25, η = 0.93, PF = 0.88
Formula: VA = HP × 746 ÷ (η × PF)
Calculation: VA = 25 × 746 ÷ (0.93 × 0.88) = 18,650 ÷ 0.8184 = 22,788 VA
An IE3 premium-efficiency motor reduces VA demand compared to a standard motor. At η = 0.85 / PF = 0.85, the same 25 HP would demand 25,813 VA—13 % more. This illustrates why high-efficiency motors reduce transformer and generator sizing requirements.
Example 6 — VA to HP: Can a 10 kVA Generator Run a 10 HP Motor?
Data: VA = 10,000, η = 0.85, PF = 0.85
Formula: HP = VA × η × PF ÷ 746
Calculation: HP = 10,000 × 0.85 × 0.85 ÷ 746 = 7,225 ÷ 746 = 9.69 HP
A 10 kVA generator can sustain only ~9.7 HP of motor load in steady state—not quite enough for a 10 HP motor. Factor in 6× starting current and the generator would need to be rated at least 30 kVA to start the motor without voltage collapse. See our Generator Load Calculator for complete sizing.
HP to VA in Electric Motors — Nameplate Context
A motor nameplate shows the mechanical output in HP (or kW), not the electrical input. To determine the electrical demand the motor places on the supply system, you must convert HP to VA using efficiency and power factor from the nameplate or manufacturer data sheet. This section explains the practical context behind each variable.
Efficiency (η): Ratio of mechanical output to electrical input (watts). A motor rated 10 HP with η = 0.91 draws 7,460 ÷ 0.91 = 8,198 W of real power from the supply. Efficiency varies from ~70 % for small fractional-HP motors to ~96 % for large IE4 machines per IEC 60034-30-1.
Power factor (PF): Ratio of real power (W) to apparent power (VA). Induction motors draw magnetizing current that doesn’t do useful work but still flows through cables and transformers. PF ranges from ~0.60 for lightly loaded small motors to ~0.92 for large motors at full load. Low PF increases VA demand, requiring larger upstream equipment.
Why VA matters more than watts for sizing: Cables, breakers, transformers, UPS units, and generators are all rated in amps—and amps are determined by VA (not watts). A 10 HP motor drawing 9,532 VA at 460 V 3-phase pulls 12 A through each phase conductor. You size the wire, breaker, and transformer for those 12 A regardless of how many of them carry real power versus reactive power.
For efficiency calculations, see our Motor Efficiency Calculator. For watt conversions, see our Amps to Watts calculator.
Quick Equivalencies — Common HP to VA Queries
1 HP to VA
~1,033 VA (typical)
At η = 85 %, PF = 0.85. With actual small-motor values (η = 82 %, PF = 0.75), 1 HP demands about 1,213 VA. Always check the nameplate.
1.5 HP to VA
~1,708 VA (typical)
Common HVAC blower motor size. At η = 84 %, PF = 0.78. Running current on 230 V 1-phase: 7.4 A.
HP to VA Calculator
VA = HP × 746 ÷ (η × PF)
Use the calculator at the top of this page. Select efficiency and power factor, and get the result instantly.
HP to VA Conversion
Multiply HP by 746, divide by η × PF
The three-step process: HP → watts → electrical watts (÷ η) → VA (÷ PF). Rule of thumb: 1 HP ≈ 1,000 VA.
VA to HP
HP = VA × η × PF ÷ 746
The inverse formula. Useful for determining how many HP of load a generator or UPS can support.
HP VA (Relationship)
1 HP = 746 W (mechanical)
HP is mechanical output; VA is electrical apparent power input. They are not directly equivalent—efficiency and power factor bridge the gap.
Horsepower to VA
VA = HP × 746 ÷ (η × PF)
Same formula. “Horsepower” and “HP” are interchangeable. 1 mechanical HP = exactly 746 watts per IEEE/NEMA definition.
HP to kVA
kVA = HP × 0.746 ÷ (η × PF)
Divide VA by 1,000 to get kVA. For a 50 HP motor at η=85%, PF=0.85: kVA = 50 × 0.746 / 0.7225 = 51.6 kVA.
HP to Volts
Not a direct conversion
HP is power; volts is potential. You cannot convert HP to volts directly. You can find the current at a given voltage: I = VA ÷ V (1-phase) or I = VA ÷ (√3 × V) (3-phase).
HP to MVA
MVA = HP × 0.000746 ÷ (η × PF)
Used for very large motors. A 1,000 HP motor at η=95%, PF=0.90 demands 0.746 / 0.855 = 0.873 MVA.
Frequently Asked Questions — HP to VA
How many VA is 1 HP?
Approximately 1,000 VA for a typical motor (η = 85 %, PF = 0.85). The exact value is VA = 746 ÷ (η × PF). With a small single-phase motor at η = 82 % and PF = 0.75, 1 HP draws about 1,213 VA.
What is the formula to convert HP to VA?
VA = HP × 746 ÷ (η × PF). Multiply the HP by 746 to get mechanical watts, then divide by efficiency and power factor to get the apparent electrical power in volt-amperes.
Can I convert HP to VA without knowing efficiency and power factor?
Not precisely. You can use the approximation 1 HP ≈ 1,000 VA for quick estimates, which assumes η ≈ 85 % and PF ≈ 0.85. For accurate sizing, always use the motor’s nameplate data.
Why is VA higher than watts for the same HP?
Because of power factor. A motor draws reactive current to magnetize its iron core. This reactive current doesn’t do useful work but still flows through cables and transformers. VA = watts ÷ PF, so VA is always ≥ watts when PF < 1.
Does the phase count affect HP to VA conversion?
No. The formula VA = HP × 746 ÷ (η × PF) applies identically to 1-phase and 3-phase motors. The phase count only matters when calculating line current from the VA result: use I = VA ÷ V for 1-phase and I = VA ÷ (√3 × V) for 3-phase.
How do I convert VA to HP?
Use HP = VA × η × PF ÷ 746. A 10 kVA UPS at η = 85 % and PF = 0.85 can supply 10,000 × 0.85 × 0.85 ÷ 746 = 9.69 HP of motor load in steady state.
How do I size a UPS for a motor using HP to VA?
First convert HP to VA using the formula. Then multiply by 1.2–1.5 for running headroom. For motor starting, multiply by 3–6 for the inrush surge. A 5 HP motor at 5,163 VA running needs a UPS rated at least 6 kVA continuous, with 15–30 kVA surge capability.
Is 1 HP always 746 watts?
Yes. 1 mechanical horsepower is defined as exactly 745.7 watts (typically rounded to 746 W). This is the shaft output power—the electrical input is always higher due to motor losses.
Why do small motors have higher VA per HP?
Small motors (under 5 HP) have lower efficiency (70–85 %) and lower power factor (0.60–0.80) than large motors. Both factors increase the denominator η × PF, which increases the VA demand per HP. A 0.5 HP motor may draw 800+ VA while a 100 HP motor draws only ~870 VA per HP.
What is the difference between HP, kW, kVA, and VA?
HP and kW measure real power (work done). VA and kVA measure apparent power (voltage × current). The difference is power factor: kW = kVA × PF. HP = kW ÷ 0.7457. For motor loads, VA is what you use to size cables, breakers, and transformers.
Can I use this formula for generators?
Yes. Generators are rated in kVA (or kW at a specified PF). Convert your motor load from HP to VA, add all loads, and select a generator with a kVA rating above the total. Add 20–30 % margin for starting surge. See our Generator Sizing Calculator.
What is a typical power factor for motors?
0.80–0.90 at full load for 3-phase induction motors. Single-phase motors are lower, typically 0.65–0.85. At partial load, PF drops significantly—a motor running at 25 % load may have PF as low as 0.40, dramatically increasing VA demand. Power-factor correction capacitors can bring PF closer to 1.0.
Related Conversions
Explore more engineering calculators on our site:
- Amps to kW Calculator — convert motor current to electrical power.
- Amps to Watts Calculator — single-phase and three-phase watt conversion.
- Amps to HP Calculator — relate motor current to horsepower rating.
- Amperes to VA Calculator — apparent power from current and voltage.
- Motor Efficiency Calculator — input vs. output power with loss breakdown.
- UPS Sizing Calculator — size UPS for servers and critical loads.
- Generator Sizing Calculator — running + starting watts for standby generators.
