How Many Amps Does a 1/8 HP single-phase Motor Draw at 240V?

Q: What is 1/8 HP in watts?

1/8 HP equals 93.25 watts of mechanical output (1 HP = 746 W). The electrical input at the terminals is higher because no motor is 100% efficient: at 85% efficiency the input is about 109.71 W.

A 1/8 HP single-phase motor at 240V draws approximately 0.5378 amps during normal operation (85% efficiency, PF 0.85). This HP and voltage combination is outside NEC Table 430.248, so there is no code-authoritative LRA multiplier for branch-circuit sizing; refer to the motor nameplate for both running current and startup characteristics.

Common applications for 1/8 HP motors: small pool pumps, light-commercial fans, booster pumps.

1/8 HP single-phase motor at 240V

0.5378 Amps running

Calculated running current at the motor terminals at the assumed 85% efficiency and PF 0.85. This is a conversion from the nameplate horsepower using those assumptions, not a measured value; a real meter reading depends on the motor's actual nameplate efficiency, loading, temperature, and motor design.

NEC Table 430.248 FLCoff-table (see nameplate)

Electrical input (HP × 746 ÷ efficiency)109.71 W

Try: 1/6HP at 240V 1/4HP at 240V 1/3HP at 240V 1/2HP at 240V

Volts

Motor Type

Running Amps (meter)

0.5378

NEC Table 430.248 FLC (code sizing)

off-table

Use the running amps for metering and energy calculations. For branch-circuit sizing, AC motors use the NEC Table 430.248 / 430.250 full-load current under NEC 430.6(A)(1); DC motors use the motor nameplate full-load current under NEC 430.6(A)(3), with Table 430.247 as the reference. Three-phase current is shown per line on a balanced circuit.

Formula (single-phase)

I_(A) = (HP × 746) ÷ (V × Eff × PF)

(1/8 × 746) ÷ (240 × 0.85 × 0.85) = 93.25 ÷ 173.4 = 0.5378 A

Convert HP to watts: 1/8 × 746 = 93.25W
Denominator: 240 × 0.85 × 0.85 = 173.4
Result: 93.25 ÷ 173.4 = 0.5378 amps

NEC Reference Values

This section lists the Code reference numbers a motor branch circuit is sized from. Final conductor, breaker, disconnect, and overload selection is an install decision a licensed electrician makes against the motor nameplate, the actual install conditions, and the applicable NEC articles, not a decision a conversion page can make for you.

Off-Table: No Code-Anchored Sizing

This combination is off-table because 1/8 HP is not a listed horsepower rating in NEC Table 430.248. The table lists discrete HP values (for three-phase: 1/2, 3/4, 1, 1½, 2, 3, 5, 7½, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, and on up), and 1/8 HP falls between listed values. 240V itself is a standard single-phase voltage in the table.

Per NEC 430.6(A)(1) Exception, when a motor rating falls between listed HP values, the next higher listed HP is used for sizing. For 1/8 HP, that means looking at 0.167 HP in the table.

Because there is no table FLC to anchor the NEC 430.22 conductor and 430.52(C)(1) OCP math, this page deliberately does not show branch-circuit sizing values for this variant. Multiplying the 0.5378 A calculated running current by 125% or 250% would produce numbers that look authoritative but are not what the code requires.

What to do instead:

Apply NEC 430.6(A)(1) Exception and size from the next higher listed HP: 0.167 HP single-phase at 240V. The table FLC shown on that page is the Code-authoritative number for your 1/8 HP branch circuit.
Pull the motor nameplate FLC and have a licensed electrician apply the 430.22 (conductor) and 430.52(C)(1) (OCP) rules against that number. NEC 430.6(A)(1) Exception permits using the next-higher listed HP where the motor rating is between table values; your inspector may also accept nameplate-based sizing for unusual HP ratings.

Operating Cost

Motor mechanical output is 93.25 W (1/8 HP × 746). Electrical input at the terminals is higher because no motor is 100% efficient: 93.25 ÷ 0.85 = 109.71 W. At $0.17/kWh, running cost is $0.02/hour or $4.48/month at 8 hours/day. Full breakdown at 109.71 W.

Amps by Motor Efficiency (single-phase)

Motor efficiency directly affects amp draw. A more efficient motor draws less current for the same HP output. Values below are the calculated single-phase running current at 240V and PF 0.85:

Efficiency	Amps at 240V	Watts Consumed	Waste Heat
75%	0.6095 A	124.33 W	31.08 W
80%	0.5714 A	116.56 W	23.31 W
85%	0.5378 A	109.71 W	16.46 W
90%	0.5079 A	103.61 W	10.36 W
95%	0.4812 A	98.16 W	4.91 W

Other HP Values at 240V (single-phase)

Running current is the calculated single-phase draw at 85% efficiency and 0.85 PF (a conversion from HP under those assumptions, not a measured value). NEC Table FLC is the value from NEC Table 430.248 used for branch-circuit conductor and OCP sizing under NEC 430.6(A)(1). LRA is estimated at 5-7× the NEC table FLC; rows outside the table show n/a because there is no code-authoritative LRA basis for that HP/voltage/phase combination. Row links open each result page in single-phase mode.

HP	Running Amps (calculated)	NEC Table 430.248 FLC	LRA Estimate (5-7× FLC)
1/8 HP	0.5378 A	off-table	n/a
1/6 HP	0.7172 A	2.2 A	11-15.4 A
1/4 HP	1.08 A	2.9 A	14.5-20.3 A
1/3 HP	1.43 A	3.6 A	18-25.2 A
1/2 HP	2.15 A	4.9 A	24.5-34.3 A
3/4 HP	3.23 A	6.9 A	34.5-48.3 A
1 HP	4.3 A	8 A	40-56 A
1.5 HP	6.45 A	10 A	50-70 A
2 HP	8.6 A	12 A	60-84 A
3 HP	12.91 A	17 A	85-119 A
5 HP	21.51 A	28 A	140-196 A
7.5 HP	32.27 A	40 A	200-280 A
10 HP	43.02 A	50 A	250-350 A
15 HP	64.53 A	off-table	n/a
20 HP	86.04 A	off-table	n/a
25 HP	107.55 A	off-table	n/a
30 HP	129.07 A	off-table	n/a
40 HP	172.09 A	off-table	n/a
50 HP	215.11 A	off-table	n/a
75 HP	322.66 A	off-table	n/a

Same HP, Other Voltages (single-phase)

speed 1/8 HP at 120V = 1.08A speed 1/8 HP at 208V = 0.6205A speed 1/8 HP at 220V = 0.5867A speed 1/8 HP at 230V = 0.5612A speed 1/8 HP at 400V = 0.3227A speed 1/8 HP at 480V = 0.2689A

Related Calculations

bolt 110W electrical input to amps at 240V payments 110W running cost

Frequently Asked Questions

How many amps does a 1/8 HP single-phase motor draw at 240V?expand_more

At the terminals, a 1/8 HP single-phase motor at 240V draws about 0.5378 amps at 85% efficiency and 0.85 power factor. This specific HP and voltage combination is outside NEC Table 430.248, so NEC branch-circuit sizing must come from the motor nameplate and a licensed electrician, not from the calculated value above.

What is 1/8 HP in watts?expand_more

1/8 HP equals 93.25 watts of mechanical output (1 HP = 746 W). The electrical input at the terminals is higher because no motor is 100% efficient: at 85% efficiency the input is about 109.71 W.

What is power factor for motors?expand_more

Motors typically run at PF 0.80-0.85 at full load. At no load, PF drops to 0.30-0.40. Low PF means the wire and breaker carry extra reactive current that does no useful mechanical work, which is why NEC motor sizing uses table FLC (which already accounts for typical PF) rather than a simple watts/volts calculation.

What branch-circuit context does a 1/8 HP single-phase motor at 240V typically sit in?expand_more

At 240V single-phase, motor branches are dedicated circuits, not general-purpose receptacles. Common NEMA configurations at this voltage are the 6-series (6-15, 6-20, 6-30, 6-50) and the 14-series (14-30, 14-50) when a neutral is needed, sized to the motor branch-circuit OCP the installer picks under NEC 430.52(C)(1). The NEC Table 430.248 FLC of is the reference number an electrician feeds into 430.22 and 430.52, not a receptacle pick on its own. Verify against the nameplate and local code.

How does NEC 430.22 size conductors for a 1/8 HP single-phase motor?expand_more

NEC 430.22 sizes branch-circuit conductors at 125% of the table full-load current, but this HP/voltage combination is not listed in NEC Table 430.248. The correct input for the 430.22 formula here is the motor nameplate FLC, applied by a licensed electrician.

This calculator provides estimates for reference purposes only. Always consult a licensed electrician and verify compliance with the National Electrical Code (NEC) and local electrical codes before performing any electrical work.