How Many Amps Does a 1/8 HP single-phase Motor Draw at 120V?

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 120V draws approximately 1.08 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 fans, bathroom exhaust, hand-held power tools.

1/8 HP single-phase motor at 120V

1.08 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 120V 1/4HP at 120V 1/3HP at 120V 1/2HP at 120V

Volts

Motor Type

Running Amps (meter)

1.08

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) ÷ (120 × 0.85 × 0.85) = 93.25 ÷ 86.7 = 1.08 A

Convert HP to watts: 1/8 × 746 = 93.25W
Denominator: 120 × 0.85 × 0.85 = 86.7
Result: 93.25 ÷ 86.7 = 1.08 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. 120V 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 1.08 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 120V. 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 120V and PF 0.85:

Efficiency	Amps at 120V	Watts Consumed	Waste Heat
75%	1.22 A	124.33 W	31.08 W
80%	1.14 A	116.56 W	23.31 W
85%	1.08 A	109.71 W	16.46 W
90%	1.02 A	103.61 W	10.36 W
95%	0.9623 A	98.16 W	4.91 W

Other HP Values at 120V (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	1.08 A	off-table	n/a
1/6 HP	1.43 A	4.4 A	22-30.8 A
1/4 HP	2.15 A	5.8 A	29-40.6 A
1/3 HP	2.87 A	7.2 A	36-50.4 A
1/2 HP	4.3 A	9.8 A	49-68.6 A
3/4 HP	6.45 A	13.8 A	69-96.6 A
1 HP	8.6 A	16 A	80-112 A
1.5 HP	12.91 A	20 A	100-140 A
2 HP	17.21 A	24 A	120-168 A
3 HP	25.81 A	34 A	170-238 A
5 HP	43.02 A	56 A	280-392 A
7.5 HP	64.53 A	80 A	400-560 A
10 HP	86.04 A	100 A	500-700 A
15 HP	129.07 A	off-table	n/a
20 HP	172.09 A	off-table	n/a
25 HP	215.11 A	off-table	n/a
30 HP	258.13 A	off-table	n/a
40 HP	344.18 A	off-table	n/a
50 HP	430.22 A	off-table	n/a
75 HP	645.33 A	off-table	n/a

Same HP, Other Voltages (single-phase)

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 240V = 0.5378A 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 120V payments 110W running cost

Frequently Asked Questions

How many amps does a 1/8 HP single-phase motor draw at 120V?expand_more

At the terminals, a 1/8 HP single-phase motor at 120V draws about 1.08 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.

Does motor efficiency affect amp draw?expand_more

Yes. A 1/8 HP single-phase motor at 90% efficiency draws 1.02 A at the terminals versus 1.22 A at 75% efficiency. Higher efficiency means lower running amps and lower electrical input wattage for the same mechanical output.

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.

How much does a 1/8 HP motor cost to run?expand_more

Operating cost is based on electrical input, not mechanical HP output. At 85% efficiency, a 1/8 HP motor draws about 109.71 W at the terminals. At $0.17/kWh (US residential average, last reviewed April 2026), that is $0.02/hour or $4.48/month at 8 hours/day.

What does NEC 430.52(C)(1) say about OCP for a 1/8 HP single-phase motor?expand_more

NEC Table 430.52(C)(1) percentages apply to the table full-load current, and this combination is not listed in NEC Table 430.248. The input for the 430.52(C)(1) math here is the motor nameplate FLC, applied by a licensed electrician with the device-type percentage that matches the install (175% dual-element fuse, 250% inverse-time breaker, 300% non-time-delay fuse, 800% instantaneous-trip breaker).

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.