How HP converts to amps
The hp to amps formula starts from one mechanical horsepower = 746 watts of shaft output. The motor's electrical input is larger
because of losses (efficiency) and, for AC, the phase shift between voltage and current (power factor).
Divide the mechanical watts by voltage — and by √3 ≈ 1.732 for three-phase — to get amps. For an hp to amps calculator 3 phase
calculation, enter the line-to-line voltage (e.g. 400, 415, 460, 480, or 575 V) and select Three-phase AC above.
DC: I = (HP × 746) ÷ V
1-phase AC: I = (HP × 746) ÷ (V × η × PF)
3-phase AC: I = (HP × 746) ÷ (√3 × V × η × PF)
Reverse — DC: HP = (I × V) ÷ 746 · 1φ: HP = (I × V × η × PF) ÷ 746 · 3φ: HP = (I × √3 × V × η × PF) ÷ 746
Worked examples
Example 1 — 10 HP, 460 V, 3-phase (eff 0.92, PF 0.85):
I = 7460 ÷ (1.732 × 460 × 0.92 × 0.85) = 7460 ÷ 623.05 ≈ 11.97 A.
Breaker hint: 11.97 × 1.25 = 14.97 → 15 A breaker; wire hint: 12 AWG copper.
Example 2 — 5 HP, 230 V, single-phase (eff 0.88, PF 0.80):
I = 3730 ÷ (230 × 0.88 × 0.80) = 3730 ÷ 161.92 ≈ 23.04 A.
Breaker hint: 23.04 × 1.25 = 28.8 → 30 A breaker; wire hint: 10 AWG copper.
Example 3 — 1 HP, 120 V DC:
I = 746 ÷ 120 ≈ 6.22 A.
Breaker hint: 6.22 × 1.25 = 7.77 → 15 A breaker; wire hint: 14 AWG copper.
Common lookups: 5 hp 230v amps ≈ 23.04 A (single-phase);
10 hp 460v amps ≈ 11.97 A (3-phase); 1 hp motor amps ≈ 1.22 A (3-phase 460 V) or
4.24 A (single-phase 230 V); 3 hp motor amps ≈ 3.67 A (3-phase 460 V).
Scope boundary
This tool converts motor horsepower ↔ amps (full-load current) — it always asks for
voltage, and for AC also efficiency and power factor.
Frequently asked questions
What is the formula to convert HP to amps?
For DC motors: I = (HP × 746) ÷ V. For single-phase AC motors: I = (HP × 746) ÷ (V × efficiency × power factor). For three-phase AC motors: I = (HP × 746) ÷ (√3 × V × efficiency × power factor), where √3 ≈ 1.732. The 746 is the watt-equivalent of one mechanical horsepower.
How do I calculate amps for a 3-phase motor?
Divide mechanical watts (HP × 746) by (√3 × line-to-line voltage × efficiency × power factor). Example: a 10 HP, 460 V, 3-phase motor with 92% efficiency and 0.85 power factor draws 7460 ÷ (1.732 × 460 × 0.92 × 0.85) ≈ 11.97 A full-load current.
How many amps does a 5 HP motor draw?
It depends on voltage and phase. With typical values (90% efficiency, 0.85 PF): a 5 HP single-phase 230 V motor draws ≈ 21.2 A; a 5 HP three-phase 460 V motor draws ≈ 6.12 A; a 5 HP DC 240 V motor draws ≈ 15.5 A. Enter your exact nameplate values in the calculator above for a precise number.
How many amps is a 1 HP motor?
Roughly: at 120 V DC ≈ 6.2 A; at 230 V single-phase (0.90 eff, 0.85 PF) ≈ 4.24 A; at 460 V three-phase (0.90 eff, 0.85 PF) ≈ 1.22 A. NEC Table 430.250 lists 2.1 A as the typical 1 HP three-phase 460 V full-load current.
Why do I need efficiency and power factor for AC motors?
Because the formula converts mechanical horsepower (shaft output) to electrical input. Efficiency (typically 0.85–0.96) accounts for motor losses, and power factor (typically 0.75–0.92) accounts for the phase shift between voltage and current in AC circuits. Ignoring both can understate the current by 20–40%.
What is full-load amps (FLA)?
Full-load amps is the current a motor draws when delivering its rated horsepower at rated voltage. It is the number used for sizing conductors, overload protection, and starters. This calculator's result IS the full-load current; the FLA table tab shows NEC published typical values.
Should I use the calculator result or the NEC table for sizing wire?
Per NEC 430.6(A), use the NEC tables (430.247–430.250) for sizing conductors, disconnects, and overcurrent protection — not the nameplate or calculated value. Use the calculator with actual nameplate efficiency and power factor when you need true operating current for energy analysis, VFD programming, or load monitoring.
How do I convert amps back to HP (reverse)?
Rearrange the same relationship: DC: HP = (I × V) ÷ 746; single-phase: HP = (I × V × efficiency × PF) ÷ 746; three-phase: HP = (I × √3 × V × efficiency × PF) ÷ 746. Use the Amps → HP tab above and enter your measured or nameplate current.
Why does a three-phase motor draw less current than a single-phase motor of the same HP?
Three-phase power is P = √3 × V × I × PF, so for the same power the current is divided by an extra √3 ≈ 1.732 factor. A 10 HP motor draws ≈ 42.4 A single-phase at 230 V but only ≈ 12.2 A three-phase at 460 V — which is why industry uses three-phase for larger motors.
What breaker size do I need for my motor?
A common rule (the 125 percent rule) is to size the branch-circuit protective device at 125% of the full-load current, rounded UP to the next standard breaker size (NEC 240.6: 15, 20, 25, 30, 35, 40, 45, 50, 60 A…). Example: 11.97 A × 1.25 = 14.97 A → 15 A breaker. Motor circuits have special NEC Article 430 rules, so confirm with a licensed electrician.
What wire size do I need for a motor circuit?
As a starting point, NEC 430.22 sizes motor branch-circuit conductors at 125% of the motor full-load current. This calculator picks the smallest copper 75°C conductor (NEC 310.16) with ampacity at or above that value — for example, 12 AWG (20 A) for ≈15 A continuous need. This is guidance only; derating, conduit fill, and local code can require larger wire.
Does this calculator work for DC motors?
Yes. Select DC mode and enter HP and voltage: I = (HP × 746) ÷ V. The DC formula here does not ask for efficiency or power factor; if your DC motor has a known efficiency below 100%, divide the result by that efficiency (e.g., 85% → result ÷ 0.85) for a more conservative current.
How is this different from an amps-to-kW calculator?
This tool starts from mechanical horsepower (shaft output) and accounts for motor efficiency and power factor. An amps-to-kW calculator starts from electrical kilowatts, which already represent electrical input. If you know kW, use our amps-to-kW calculator; if you know HP, you are in the right place.
What are typical efficiency and power factor values for motors?
Small motors (1–5 HP): efficiency ≈ 0.80–0.90, PF ≈ 0.75–0.85. Medium motors (7.5–30 HP): efficiency ≈ 0.87–0.93, PF ≈ 0.82–0.90. Large motors (40–200 HP) and NEMA Premium/IE3: efficiency ≈ 0.91–0.96, PF ≈ 0.85–0.92. Motors running at partial load have lower power factor. When in doubt, use the calculator defaults (0.90 / 0.85) and check the nameplate.
Is this calculator free and does it work offline?
Yes — it is 100% client-side. All calculations run in your browser with no data sent anywhere, so it works offline once the page is loaded. There are no accounts, no ads in the calculation area, and no external requests.
Can I trust this for actual electrical installation work?
The math is exact, but real installations must comply with the NEC (or your local code) and Article 430 motor rules — table values, 125% sizing, disconnect means, and short-circuit protection. This calculator is a design aid; final circuit design should be done or reviewed by a licensed electrician.