Wire Gauge Calculator

Circuit type:

Choose the circuit model before sizing the voltage drop.

Load current:

Enter the current that the conductor must carry.

One-way run length:

Use the one-way cable run, not the round-trip total.

System voltage:

Use nominal line voltage for the load, such as 12, 24, 48, 120, or 240 volts.

Maximum voltage drop:

Set the largest acceptable drop from source to load.

Conductor material:

Choose the conductor material for resistance and ampacity checks.

Ampacity temperature column:

Select the conductor temperature rating to use for this planning check.

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Load sizing margin:

Use 100% for the entered load, or raise it when a design margin applies.

Comparison gauge:

Adds a selected-gauge line to the snapshot and JSON without changing the recommendation.

Decimal places:

Use 0-6 places for displayed numbers and exports.

places

Metric	Value	Sizing note	Copy
{{ row.metric }}	{{ row.value }}	{{ row.note }}

Gauge	Ampacity	Voltage drop	Drop percent	Resistance	Status	Copy
{{ row.gauge }}	{{ row.ampacity }}	{{ row.voltageDrop }}	{{ row.dropPercent }}	{{ row.resistance }}	{{ row.status }}

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A wire that is too small can pass current for a short time and still be the wrong conductor for the job. Heat, voltage loss, terminal ratings, insulation temperature, and the length of the run all affect whether power reaches the load safely and with enough voltage left to do useful work. The awkward part is that these limits do not always point to the same size.

American Wire Gauge, or AWG, is the size scale commonly used for smaller electrical conductors in North America. It runs backward from everyday counting: 14 AWG is smaller than 12 AWG, 8 AWG is larger than 10 AWG, and the large "aught" sizes such as 1/0 through 4/0 continue beyond 1 AWG. Each step changes conductor diameter by a fixed ratio, so a few gauge numbers can make a large difference in resistance, heat, and voltage drop.

Wire sizing usually starts with two separate questions. Ampacity asks whether the conductor can carry the design current under the reference conditions being used. Voltage drop asks how much voltage is lost in the conductor before the load sees it. A conductor can pass one question and fail the other, especially on low-voltage or long-distance circuits.

Low-voltage systems make voltage drop visible sooner because the same lost volts are a larger share of the supply. A drop of 0.4 V is minor on a 120 V circuit but more than 3% on a 12 V circuit. Solar wiring, battery equipment, LED lighting, control runs, pumps, motors, and electronics can therefore need a larger wire than ampacity alone would suggest.

Material choice also changes the answer. Copper has lower resistance than aluminum for the same cross-sectional area, while aluminum conductors often need a larger gauge to carry the same load or hold the same voltage drop. Temperature ratings matter because ampacity tables are organized by conductor and termination temperature, and conductor resistance rises as temperature rises.

Common wire sizing influences
Influence	Why it can change the gauge
Current	More current raises voltage drop and makes ampacity limits harder to satisfy.
One-way run length	Longer cable means more conductor resistance in the electrical path.
System voltage	Lower voltage makes each lost volt a larger percentage of the supply.
Material and temperature	Resistance and reference ampacity depend on conductor material and the selected temperature column.

A calculated AWG size is best treated as a planning candidate. Real installations still need the applicable electrical code, conductor insulation type, breaker or fuse rules, terminal temperature limits, derating for ambient heat or grouped conductors, raceway fill, equipment instructions, and local inspection requirements.

How to Use This Tool:

Choose the circuit type first. DC and single-phase checks use an out-and-back path, while the three-phase option uses a line-to-line path multiplier.
Enter the load current, the one-way source-to-load run length, the nominal system voltage, and the maximum voltage-drop percentage you want to allow.
Select copper or aluminum, then choose the 60 C, 75 C, or 90 C ampacity temperature column that matches the planning reference you intend to check.
Open Advanced when the ampacity check needs a load sizing margin, when you want to compare a known gauge, or when the displayed decimal precision should change. The margin changes design current for ampacity only; voltage drop uses the entered load current.
Start with the Wire Size Check. Use the Gauge Candidate Ledger to see each AWG pass or fail reason, then use the Voltage Drop Map and JSON view when you need a chart or structured export.

Interpreting Results:

The recommended wire gauge is the smallest listed AWG size that passes both the voltage-drop limit and the reference ampacity check. If no listed size through 4/0 passes, the result points outside the calculator's AWG range and the circuit needs a different design review, such as a shorter run, higher voltage, parallel conductors where allowed, or a larger conductor family.

Read the voltage drop as both volts and percent. The volts show the estimated conductor loss over the modeled electrical path. The percent tells you how large that loss is compared with the system voltage, which is usually the better way to compare a 12 V run with a 120 V or 240 V run.

The candidate ledger explains the limiting condition. "Voltage drop fail" means the conductor has enough listed ampacity for the margin-adjusted design current but loses too much voltage over the path. "Ampacity fail" means the selected reference ampacity is below the design current. "No ampacity reference" means the geometry can be modeled but that material and gauge are not covered by the ampacity table used here.

The comparison gauge is an inspection aid, not an override. It lets you test an existing or preferred size against the same assumptions while leaving the recommendation based on the smallest passing listed conductor.

Technical Details:

AWG geometry follows a logarithmic scale. The diameter changes by a constant ratio from one gauge number to the next, and cross-sectional area changes with the square of diameter. Because resistance is inversely proportional to area, a larger conductor reduces voltage drop and I squared R heating for the same load current.

Voltage-drop sizing is an Ohm's law calculation over the electrical path. The entered length is one-way physical distance, then the circuit model supplies the path multiplier. DC, two-wire, and single-phase cases use a multiplier of 2 for the outgoing and return conductors. The three-phase estimate uses sqrt(3) for balanced line-to-line voltage drop.

Ampacity is checked separately from modeled resistance. The resistance calculation can estimate voltage loss from geometry and material constants, but the allowed current comes from a reference table for the chosen material, gauge, and temperature column. A candidate conductor has to pass both checks before it is recommended.

Formula Core:

\begin{array}{lcl} d_{n} & = & 0.127 \times 92^{\frac{36 - n}{39}} mm \\ A & = & π {(\frac{d}{2})}^{2} \\ ρ_{T} & = & ρ_{20} [1 + α (T - 20)] \\ R_{path} & = & \frac{ρ_{T}}{A} \times L \times k \\ V_{drop} & = & I \times R_{path} \\ drop% & = & 100 \times \frac{V_{drop}}{V_{system}} \end{array}

Wire gauge formula symbols
Symbol	Meaning
n	AWG gauge number. The larger aught sizes are represented as 0 for 1/0, -1 for 2/0, -2 for 3/0, and -3 for 4/0 in the diameter formula.
L	One-way run length converted to meters before the circuit multiplier is applied.
k	Electrical path multiplier: 2 for DC, two-wire, and single-phase cases, or sqrt(3) for three-phase.
I	Load current in amperes for voltage drop. The margin-adjusted design current is used for ampacity.
T	Selected 60 C, 75 C, or 90 C column used for resistance temperature adjustment and ampacity lookup.

Wire gauge model constants and pass rules
Item	Model used
Copper resistance	1.724e-8 ohm-meter at 20 C, adjusted by a temperature coefficient of 0.00393 per C.
Aluminum resistance	2.82e-8 ohm-meter at 20 C, adjusted by a temperature coefficient of 0.00403 per C.
Gauge range	Standard listed sizes from 18 AWG through 4/0 are tested. Aluminum ampacity references begin at 12 AWG.
Pass condition	Reference ampacity must be at least the design current, and voltage-drop percent must be less than or equal to the entered limit.

Substitution Example:

With the default-style setup of 10 A, 15 ft one-way, 12 V, copper, a 3% voltage-drop limit, and the 75 C column, the path is about 9.14 m because the DC out-and-back multiplier doubles the one-way distance. At 8 AWG the modeled drop is about 0.23 V, or about 1.91%, and the 50 A reference ampacity clears the 10 A design current when the load margin is 100%.

Displayed precision only affects the numbers shown in tables, chart labels, and exports. Pass and fail decisions are made from the underlying calculated values, so a rounded value that appears exactly at the limit should still be treated as a close result.

Accuracy and Privacy Notes:

Resistance estimates use ideal round-conductor AWG geometry and material constants. Real cable resistance can differ because of stranding, alloy, manufacturing tolerance, operating temperature, cable construction, and manufacturer data. The ampacity check is a reference screen, not a full code calculation.

Final conductor approval can change after ambient-temperature correction, more than three current-carrying conductors, cables grouped together, raceway fill, rooftop exposure, terminal limits, conductor insulation type, continuous-load rules, and local code requirements are applied. Safety-critical or code-governed work should be confirmed with the governing standard, product instructions, and a qualified electrical professional.

The calculation runs in the browser from the values entered on the page. Copies, CSV files, chart images, DOCX exports, and JSON downloads are generated from the visible result data rather than from a remote calculation service.

Worked Examples:

Wire gauge calculation examples
Scenario	Inputs	Result to check
Short low-voltage DC load	10 A, 15 ft one-way, 12 V, 3% drop limit, copper, 75 C column.	8 AWG passes at about 0.23 V drop, or 1.91%, with 50 A reference ampacity.
Long 120 V branch estimate	20 A, 75 ft one-way, 120 V, 3% drop limit, copper, 75 C column.	8 AWG keeps the modeled drop near 2.29 V, or 1.91%, and passes the selected ampacity reference.
Three-phase aluminum check	40 A, 60 ft one-way, 240 V, 3% drop limit, aluminum, 75 C column.	8 AWG passes at about 5.22 V drop, or 2.17%, with 40 A reference ampacity in that column.
Existing-cable comparison	Keep the calculated inputs, then set Comparison gauge to a known installed size.	The recommendation stays unchanged while the selected gauge row shows its own drop percent, ampacity reference, and pass/fail status.

FAQ:

Why can a larger wire be needed even when ampacity passes?

Ampacity checks heating under a reference current limit. Voltage drop checks loss over distance. Long runs and low-voltage loads can fail the voltage-drop check even when the conductor's reference ampacity is high enough.

Does the load sizing margin change voltage drop?

No. Voltage drop is calculated from the entered operating current. The margin is applied to the design current used for the ampacity pass/fail check.

Why are smaller aluminum gauges missing ampacity references?

The aluminum reference table used by the calculator starts at 12 AWG. Smaller aluminum sizes can still have calculated geometry and resistance, but they are not treated as passing candidates without a listed ampacity value.

Is 3% always the required voltage-drop limit?

No. Three percent is a common planning target for many branch-circuit checks, while some low-voltage, motor, charger, lighting, or sensitive-electronics loads may need a tighter target. Local rules and equipment instructions can differ.

Can this result replace an electrical code review?

No. The result is a conductor-size screening estimate. Breaker sizing, allowed conductor type, terminal ratings, derating, installation method, and local code still have to be checked separately.

Glossary:

AWG: American Wire Gauge, a reverse-numbered conductor size scale where smaller numbers mean larger conductors.
Ampacity: The current a conductor can carry under specified reference conditions without exceeding its temperature rating.
Voltage drop: The voltage lost across conductor resistance while current flows from the source to the load.
One-way run: The physical distance from source to load before the circuit path multiplier accounts for return conductors or three-phase line-to-line behavior.
Design current: The current used for the ampacity check after the load sizing margin is applied.
1/0 through 4/0: Large AWG sizes above 1 AWG, commonly read as one-aught through four-aught.