Wire Size Input Form
Formula Used
Single phase or DC voltage drop: Vdrop = 2 x L x I x R / 1000
Three phase voltage drop: Vdrop = 1.732 x L x I x R / 1000
Drop percent: Drop percent = Vdrop / Voltage x 100
Adjusted ampacity: Adjusted ampacity = Base ampacity x ambient factor x bundling factor x rating factor
Design current: Design current = Load current x continuous factor x safety factor
L is one way length in feet. I is design current. R is conductor resistance in ohms per 1000 feet.
How to Use This Calculator
Enter known current when the load amperage is available. Choose power mode when you know watts instead.
Enter the system voltage and one way wire length. Select circuit type, material, and voltage drop target.
Add ambient temperature, conductor count, insulation rating, and continuous load status. Press calculate.
Read the recommended gauge above the form. Download CSV or PDF when you need a saved result.
Example Data Table
| Example | Voltage | Current | Length | Material | Drop Limit | Typical Result |
|---|---|---|---|---|---|---|
| Small lighting run | 120 V | 8 A | 40 ft | Copper | 3% | 14 AWG |
| Workshop outlet | 120 V | 20 A | 75 ft | Copper | 3% | 8 AWG |
| Three phase motor | 480 V | 35 A | 150 ft | Copper | 3% | 6 AWG |
| Feeder estimate | 240 V | 60 A | 100 ft | Aluminum | 3% | 2 AWG |
Wire Size Planning Basics
A wire size calculator helps estimate a conductor for a planned load. It uses current, voltage, length, material, and allowed voltage drop. The result is not a permit drawing. It is a planning guide for early sizing work. Final wiring must follow local code and a qualified electrician.
Why AWG Matters
AWG numbers move opposite to size. A smaller gauge number means a larger conductor. Larger conductors have lower resistance. Lower resistance reduces heat and voltage loss. This matters on long runs, motor loads, outdoor feeders, battery systems, and low voltage circuits.
Voltage Drop Control
Voltage drop is the voltage lost in the conductors. A long run loses more voltage. A higher current loses more voltage. Copper usually loses less than aluminum at the same gauge. Many designers aim for three percent drop on branch circuits. Some sensitive loads need less drop. This tool lets you set your own limit.
Ampacity and Conditions
Ampacity is the current a conductor can carry under rated conditions. Real installations may reduce that value. Hot ambient air can lower safe capacity. Several current carrying conductors in one raceway can also lower it. Continuous loads often need extra margin. The calculator applies simple derating choices, then compares the adjusted ampacity with the design current.
Using the Estimate
Start with the load current. Use the real one way distance, not round trip distance. Select the wiring material and circuit type. Choose the voltage drop target. Add temperature and bundling factors when known. The tool checks common AWG sizes. It selects the first gauge that satisfies adjusted ampacity and voltage drop.
Reading the Output
The result shows design current, estimated drop, wire resistance, and recommended gauge. It also gives an alternate gauge for comparison when available. Export the result to CSV for spreadsheets. Use the PDF option for a simple project record. Keep the example table nearby when learning how inputs change the answer. Record assumptions on every export so later reviews stay clear and traceable for teams.
Safety Note
This calculator does not replace code tables, manufacturer data, conduit fill rules, terminal temperature limits, or inspection requirements. Use it for estimates. Confirm every final installation with applicable standards and a licensed professional.
FAQs
1. What does AWG mean?
AWG means American Wire Gauge. It is a numbering system for conductor size. Smaller AWG numbers mean larger wires. Larger wires usually carry more current and have lower voltage drop.
2. Is a smaller AWG number bigger?
Yes. For example, 10 AWG is physically larger than 14 AWG. It has lower resistance and can usually carry more current, depending on material and installation conditions.
3. Why does wire length affect size?
Longer wire has more resistance. More resistance causes more voltage drop. The calculator may recommend a larger wire when the run is long, even when ampacity already passes.
4. What voltage drop should I use?
Many planning estimates use three percent for branch circuits. Sensitive electronics, motors, and low voltage systems may need a smaller limit. Always follow project requirements and local rules.
5. Does aluminum need a larger size?
Usually yes. Aluminum has higher resistance than copper. For the same current and length, aluminum often needs a larger conductor to meet ampacity and voltage drop goals.
6. What is continuous load sizing?
A continuous load runs for a long period. Many designs add a 125 percent factor. This calculator applies that factor when the continuous load option is selected.
7. Can this replace an electrician?
No. This tool gives estimates only. Final wiring must consider codes, breaker size, insulation, terminals, conduit fill, environment, and inspection rules.
8. Why is ampacity derating included?
Heat reduces safe current capacity. High ambient temperature and bundled conductors can require derating. The calculator includes simple factors to make planning more realistic.