Reference tables

Voltage Drop Chart

A voltage drop chart is only as good as the numbers behind it. Every figure on this page is either computed live by the same engine the calculators use, or cited to the table it came from. Nothing is transcribed from another chart.

Voltage drop percentage on a 120 V single-phase circuit at 20 A, copper conductors in AWG sizes, one-way distance. Anything above 3% is marked.

Voltage drop percentage by conductor size and one-way distance
Size	25 ft	50 ft	75 ft	100 ft	150 ft	200 ft	250 ft	300 ft	400 ft	500 ft
14 AWG	2.62%	5.23%, over limit	7.85%, over limit	10.47%, over limit	15.70%, over limit	20.93%, over limit	26.17%, over limit	31.40%, over limit	41.87%, over limit	52.33%, over limit
12 AWG	1.65%	3.30%, over limit	4.95%, over limit	6.60%, over limit	9.90%, over limit	13.20%, over limit	16.50%, over limit	19.80%, over limit	26.40%, over limit	33.00%, over limit
10 AWG	1.03%	2.07%	3.10%, over limit	4.13%, over limit	6.20%, over limit	8.27%, over limit	10.33%, over limit	12.40%, over limit	16.53%, over limit	20.67%, over limit
8 AWG	0.65%	1.30%	1.95%	2.59%	3.89%, over limit	5.19%, over limit	6.48%, over limit	7.78%, over limit	10.37%, over limit	12.97%, over limit
6 AWG	0.41%	0.82%	1.23%	1.64%	2.46%	3.27%, over limit	4.09%, over limit	4.91%, over limit	6.55%, over limit	8.18%, over limit
4 AWG	0.26%	0.51%	0.77%	1.03%	1.54%	2.05%	2.57%	3.08%, over limit	4.11%, over limit	5.13%, over limit
3 AWG	0.20%	0.41%	0.61%	0.82%	1.23%	1.63%	2.04%	2.45%	3.27%, over limit	4.08%, over limit
2 AWG	0.16%	0.32%	0.48%	0.65%	0.97%	1.29%	1.62%	1.94%	2.59%	3.23%, over limit
1 AWG	0.13%	0.26%	0.38%	0.51%	0.77%	1.03%	1.28%	1.54%	2.05%	2.57%
1/0 AWG	0.10%	0.20%	0.31%	0.41%	0.61%	0.81%	1.02%	1.22%	1.63%	2.03%
2/0 AWG	0.08%	0.16%	0.24%	0.32%	0.48%	0.64%	0.81%	0.97%	1.29%	1.61%
3/0 AWG	0.06%	0.13%	0.19%	0.26%	0.38%	0.51%	0.64%	0.77%	1.02%	1.28%
4/0 AWG	0.05%	0.10%	0.15%	0.20%	0.30%	0.41%	0.51%	0.61%	0.81%	1.01%

Computed with the site calculator from NEC Chapter 9, Table 8 direct-current resistance at 75 °C. Resistance only. See the AC calculator for results including conductor reactance.

Per amp, per 100 ft

The figure you can do arithmetic with.

Volts dropped per ampere per 100 ft of one-way run on a two-wire circuit. Multiply by your current and by your run length in hundreds of feet, and you have the drop in volts.

Voltage drop per ampere per 100 ft for copper and aluminium conductors
Size	Area	Circular mils	Copper	Aluminium	Al ÷ Cu
18 AWG	0.82 mm²	1,620	1.59 V	2.62 V	1.65×
16 AWG	1.31 mm²	2,580	0.998 V	1.642 V	1.65×
14 AWG	2.08 mm²	4,110	0.628 V	1.034 V	1.65×
12 AWG	3.31 mm²	6,530	0.396 V	0.65 V	1.64×
10 AWG	5.26 mm²	10,380	0.248 V	0.408 V	1.65×
8 AWG	8.37 mm²	16,510	0.1556 V	0.256 V	1.65×
6 AWG	13.30 mm²	26,240	0.0982 V	0.1616 V	1.65×
4 AWG	21.15 mm²	41,740	0.0616 V	0.1016 V	1.65×
2 AWG	33.62 mm²	66,360	0.0388 V	0.0638 V	1.64×
1/0 AWG	53.49 mm²	105,600	0.0244 V	0.0402 V	1.65×
2/0 AWG	67.43 mm²	133,100	0.01934 V	0.0318 V	1.64×
4/0 AWG	107.20 mm²	211,600	0.01216 V	0.02 V	1.64×
250 kcmil	127.00 mm²	250,000	0.0103 V	0.01694 V	1.64×
500 kcmil	253.00 mm²	500,000	0.00516 V	0.00848 V	1.64×

Computed as 2 × R × 0.1 from NEC Chapter 9, Table 8 direct-current resistance at 75 °C, Class B stranded. For three-phase, multiply by √3 ÷ 2 = 0.866.

Conductor resistance

AWG and kcmil sizes.

Direct-current resistance at 75 °C, per conductor. Both stranding classes are listed for the sizes manufactured either way.

Conductor resistance for AWG and kcmil sizes, copper and aluminium
Size	mm²	Cu solid Ω/kft	Cu stranded Ω/kft	Cu stranded Ω/km	Al stranded Ω/kft	Al stranded Ω/km
18 AWG	0.82	7.77	7.95	26.08	13.1	42.98
16 AWG	1.31	4.89	4.99	16.37	8.21	26.94
14 AWG	2.08	3.07	3.14	10.3	5.17	16.96
12 AWG	3.31	1.93	1.98	6.496	3.25	10.66
10 AWG	5.26	1.21	1.24	4.068	2.04	6.693
8 AWG	8.37	0.764	0.778	2.552	1.28	4.199
6 AWG	13.30	—	0.491	1.611	0.808	2.651
4 AWG	21.15	—	0.308	1.01	0.508	1.667
3 AWG	26.67	—	0.245	0.8038	0.403	1.322
2 AWG	33.62	—	0.194	0.6365	0.319	1.047
1 AWG	42.41	—	0.154	0.5052	0.253	0.8301
1/0 AWG	53.49	—	0.122	0.4003	0.201	0.6594
2/0 AWG	67.43	—	0.0967	0.3173	0.159	0.5217
3/0 AWG	85.01	—	0.0766	0.2513	0.126	0.4134
4/0 AWG	107.20	—	0.0608	0.1995	0.1	0.3281
250 kcmil	127.00	—	0.0515	0.169	0.0847	0.2779
300 kcmil	152.00	—	0.0429	0.1407	0.0707	0.232
350 kcmil	177.00	—	0.0367	0.1204	0.0605	0.1985
400 kcmil	203.00	—	0.0321	0.1053	0.0529	0.1736
500 kcmil	253.00	—	0.0258	0.08465	0.0424	0.1391
600 kcmil	304.00	—	0.0214	0.07021	0.0353	0.1158
700 kcmil	355.00	—	0.0184	0.06037	0.0303	0.09941
750 kcmil	380.00	—	0.0171	0.0561	0.0282	0.09252
800 kcmil	405.00	—	0.0161	0.05282	0.0265	0.08694
900 kcmil	456.00	—	0.0143	0.04692	0.0235	0.0771
1000 kcmil	507.00	—	0.0129	0.04232	0.0212	0.06955

NFPA 70 (National Electrical Code), Chapter 9, Table 8 (Conductor Properties). Direct-current resistance at 75 °C (167 °F). Values there are calculated per National Bureau of Standards Handbook 100 (1966) and Handbook 109 (1972), at 100% IACS for copper and 61% IACS for aluminium.

Conductor resistance

Metric mm² sizes.

These are calculated, not looked up. No published table on this site covers IEC conductor sizes, so the figures come from resistivity, and the page says so rather than presenting them as tabulated values.

Calculated conductor resistance for metric sizes, copper and aluminium
Size	Circular mils	Copper Ω/km	Copper Ω/kft	Aluminium Ω/km	Aluminium Ω/kft
0.5 mm²	987	41.94	12.78	69.06	21.05
0.75 mm²	1,480	27.96	8.521	46.04	14.03
1 mm²	1,974	20.97	6.391	34.53	10.52
1.5 mm²	2,960	13.98	4.261	23.02	7.016
2.5 mm²	4,934	8.387	2.556	13.81	4.21
4 mm²	7,894	5.242	1.598	8.632	2.631
6 mm²	11,841	3.495	1.065	5.755	1.754
10 mm²	19,735	2.097	0.6391	3.453	1.052
16 mm²	31,576	1.31	0.3994	2.158	0.6578
25 mm²	49,338	0.8387	0.2556	1.381	0.421
35 mm²	69,073	0.5991	0.1826	0.9865	0.3007
50 mm²	98,676	0.4194	0.1278	0.6906	0.2105
70 mm²	138,147	0.2995	0.0913	0.4933	0.1503
95 mm²	187,485	0.2207	0.06727	0.3635	0.1108
120 mm²	236,823	0.1747	0.05326	0.2877	0.0877
150 mm²	296,029	0.1398	0.04261	0.2302	0.07016
185 mm²	365,102	0.1133	0.03455	0.1866	0.05689
240 mm²	473,646	0.08737	0.02663	0.1439	0.04385
300 mm²	592,058	0.06989	0.0213	0.1151	0.03508
400 mm²	789,410	0.05242	0.01598	0.08632	0.02631
500 mm²	986,763	0.04194	0.01278	0.06906	0.02105

Calculated as R = ρ₂₀ × [1 + α₂₀ × (T − 20)] ÷ A at 75 °C, with ρ₂₀ = 1.7241 × 10⁻⁸ Ω·m for copper (100% IACS) and 2.8264 × 10⁻⁸ Ω·m for aluminium (61% IACS). This models a smooth conductor of the nominal area; real stranded cable reads roughly 2% higher because the strands spiral, and IEC 60228 maximum values allow more again. The same method reproduces NEC Chapter 9 Table 8 solid-conductor values to within 0.2%.

AC values

Resistance and reactance at 60 Hz.

For AC circuits below unity power factor, resistance alone understates the drop. These are the values the AC calculator combines into an effective impedance.

AC resistance and inductive reactance by conductor size and raceway
Size	X_L PVC/Al	X_L steel	Cu R, PVC	Cu R, steel	Al R, PVC	Al R, steel
14 AWG	0.058	0.073	3.1	3.1	—	—
12 AWG	0.054	0.068	2	2	3.2	3.2
10 AWG	0.05	0.063	1.2	1.2	2	2
8 AWG	0.052	0.065	0.78	0.78	1.3	1.3
6 AWG	0.051	0.064	0.49	0.49	0.81	0.81
4 AWG	0.048	0.06	0.31	0.31	0.51	0.51
3 AWG	0.047	0.059	0.25	0.25	0.4	0.4
2 AWG	0.045	0.057	0.19	0.2	0.32	0.32
1 AWG	0.046	0.057	0.15	0.16	0.25	0.25
1/0 AWG	0.044	0.055	0.12	0.12	0.2	0.2
2/0 AWG	0.043	0.054	0.1	0.1	0.16	0.16
3/0 AWG	0.042	0.052	0.077	0.079	0.13	0.13
4/0 AWG	0.041	0.051	0.062	0.063	0.1	0.1
250 kcmil	0.041	0.052	0.052	0.054	0.085	0.086
300 kcmil	0.041	0.051	0.044	0.045	0.071	0.072
350 kcmil	0.04	0.05	0.038	0.039	0.061	0.063
400 kcmil	0.04	0.049	0.033	0.035	0.054	0.055
500 kcmil	0.039	0.048	0.027	0.029	0.043	0.045
600 kcmil	0.039	0.048	0.023	0.025	0.036	0.038
750 kcmil	0.038	0.048	0.019	0.021	0.029	0.031
1000 kcmil	0.037	0.046	0.015	0.018	0.023	0.025

NFPA 70, Chapter 9, Table 9, Alternating-Current Resistance and Reactance for 600-Volt Cables, 3-Phase, 60 Hz, 75 °C, three single conductors in conduit. Ohms to neutral per 1000 ft, Class B stranded RHH in a cradled configuration. Capacitive reactance is ignored as negligible at these voltages. Effective Z is computed as R cos θ + X sin θ at 0.85 power factor.

Ampacity

What each size may carry.

A separate question from voltage drop, included here because a conductor has to satisfy both. These are base table values before any correction or adjustment factor.

Allowable ampacity by conductor size, material and temperature rating
Size	Cu 60 °C	Cu 75 °C	Cu 90 °C	Al 60 °C	Al 75 °C	Al 90 °C
14 AWG	15	20	25	—	—	—
12 AWG	20	25	30	15	20	25
10 AWG	30	35	40	25	30	35
8 AWG	40	50	55	35	40	45
6 AWG	55	65	75	40	50	55
4 AWG	70	85	95	55	65	75
3 AWG	85	100	115	65	75	85
2 AWG	95	115	130	75	90	100
1 AWG	110	130	145	85	100	115
1/0 AWG	125	150	170	100	120	135
2/0 AWG	145	175	195	115	135	150
3/0 AWG	165	200	225	130	155	175
4/0 AWG	195	230	260	150	180	205
250 kcmil	215	255	290	170	205	230
300 kcmil	240	285	320	195	230	260
350 kcmil	260	310	350	210	250	280
400 kcmil	280	335	380	225	270	305
500 kcmil	320	380	430	260	310	350
600 kcmil	350	420	475	285	340	385
750 kcmil	400	475	535	320	385	435
1000 kcmil	455	545	615	375	445	500

NFPA 70, Table 310.16. Allowable ampacities of insulated conductors rated up to 2000 V, not more than three current-carrying conductors in a raceway, cable or earth, at 30 °C (86 °F) ambient. Correction factors for ambient temperature, adjustment factors for conductor count, terminal temperature limitations under 110.14(C), and the small-conductor rules of 240.4(D) are not applied.

How to read these charts

Distance is one-way

Every distance in these tables is the distance from the source to the load. The formulas already double it for the return conductor. Entering a total cable length as if it were a one-way figure is the most common way to get an answer that is twice what it should be.

Resistance is at 75 °C

Conductor resistance rises with temperature. A conductor running cool drops less than these figures show, one running hot drops more. The main calculator applies the NEC Chapter 9 Table 8 Note 2 correction if you tell it the operating temperature.

Reactance is not included in the matrix

The size-by-distance chart uses resistance only. That is exact for DC and for AC at unity power factor. For inductive loads, use the AC calculator, which combines resistance and reactance at your power factor.

These are calculations, not measurements

A real run also has resistance at every termination, splice and device. Expect a measured drop somewhat higher than a calculated one. If it is far higher, the problem is usually a connection rather than the conductor. See how to measure voltage drop.

Questions

Common questions.

How do you read a voltage drop chart?

Find the row for your conductor size and the column for your material or distance, and read the figure. The tables here give volts dropped per ampere per 100 ft, so multiply the figure by your load current and by your run length in hundreds of feet. A 10 AWG copper conductor at 0.24 V per amp per 100 ft carrying 15 A over 60 ft drops 0.24 × 15 × 0.6 = 2.16 V.

What is the voltage drop per 100 feet of wire?

It depends on the conductor size, the material and the current, which is why a chart is indexed by size rather than giving one number. The per-ampere figure is fixed for a given size and material, so the chart states that and you supply the current. Doubling the current doubles the drop, and doubling the conductor area roughly halves it.

Are voltage drop charts accurate?

They are accurate for the conditions they were built on and only those. The tables here assume 75 °C conductor temperature, resistance only with no reactance term, and the distance measured one way. A run at a different temperature, an inductive load below unity power factor, or a large conductor in steel conduit will differ. Use a chart to narrow the choice and the calculator to confirm it.

What is the difference between a voltage drop chart and a wire size chart?

A voltage drop chart starts from a conductor size and tells you the drop it produces. A wire size chart works the other way, starting from a load and a distance and giving a size that will meet a stated drop limit. They answer opposite questions from the same underlying data, and a wire size figure always carries an assumed voltage, current and drop limit that has to match your circuit for the answer to hold.

More tools

Other calculators.

DC · 1Ø · 3ØVoltage Drop CalculatorThe main calculator. DC, single-phase and three-phase, with reactance and temperature correction when you need them.12 V · 24 V · 48 VDC Voltage Drop CalculatorBattery, solar and automotive circuits at 12 V, 24 V and 48 V, where a few tenths of a volt matter.R + jX · PFAC Voltage Drop CalculatorSingle-phase and three-phase with power factor, conductor reactance and raceway type.mm² · metresCable Voltage Drop CalculatorCable runs in metres and conductor sizes in mm², for anyone working to metric cable data rather than AWG.AWG · kcmil · mm²Wire Size CalculatorThe smallest conductor that stays inside your drop limit, shown against the ampacity the size carries.L maxMaximum Cable Length CalculatorHow far you can run a given conductor before the drop crosses your limit.V = I × RResistor Voltage Drop CalculatorOhm’s law solved for voltage, current or resistance, with power dissipation and a series divider.TablesVoltage Drop ChartDrop per amp per 100 ft for every size and material, plus conductor resistance and ampacity tables.