Estimate wire size using load, length, and drop. Check copper and aluminum options with derating. Get results, formulas, examples, FAQs, and printable exports fast.
| Scenario | Voltage | Load | Length | Material | Suggested Size |
|---|---|---|---|---|---|
| Kitchen appliance circuit | 230 V | 3500 W | 25 m | Copper | 10 AWG / 5.26 mm² |
| Water heater branch circuit | 230 V | 4500 W | 18 m | Copper | 10 AWG / 5.26 mm² |
| Detached room feeder | 230 V | 7200 W | 35 m | Aluminum | 4 AWG / 21.2 mm² |
Single phase current: I = P / (V × PF)
Three phase current: I = P / (√3 × V × PF)
Demand adjusted current: Id = I × Demand Factor
Continuous load adjustment: Ic = Id × 1.25 when continuous load is selected.
Design current: Idesign = Ic × (1 + Safety Margin)
Effective ampacity: Aeffective = Base Ampacity × Temperature Factor × Bundling Factor
Single phase voltage drop: Vd = 2 × L × I × R / 1000
Three phase voltage drop: Vd = √3 × L × I × R / 1000
Voltage drop percent: Vd% = (Vd / Supply Voltage) × 100
The tool selects the smallest listed conductor that passes both ampacity and voltage drop checks.
A home wire size calculator helps plan safer household circuits. It converts electrical load into practical conductor choices. The tool checks current, voltage drop, and material resistance. It also considers derating. That matters when wires run through warm spaces or grouped conduits. A correct estimate reduces nuisance trips, overheating risk, and wasted energy. It also supports cleaner installation planning before buying cable, conduit, breakers, and boxes. Good sizing improves performance and keeps connected devices operating with steadier voltage during normal daily use.
Wire size starts with load current. Single phase circuits use power divided by voltage and power factor. Three phase loads use the square root of three. After that, design current is adjusted by demand, continuity, and safety margin. Continuous loads usually need extra allowance. Ambient temperature and grouped circuits reduce usable ampacity. The calculator applies these derating factors before recommending a conductor. It then compares voltage drop against the chosen limit. That keeps long runs from causing dim lights, hot motors, and weak appliance performance.
Copper usually carries more current for the same cross sectional area. It also has lower resistance. Aluminum can still work well when properly sized. It is lighter and often lower in cost. Because its resistance is higher, it commonly needs a larger conductor. The calculator compares both materials using practical resistance and ampacity values. This helps homeowners, installers, and students review options quickly. It also makes tradeoffs easier to understand when balancing cable size, distance, load growth, and breaker selection.
Use the form with realistic values. Enter system voltage, run length, and either load power or current. Then add power factor, demand factor, and allowed voltage drop. Choose conductor material and ambient conditions. Submit the form to see the recommended wire, estimated breaker, and drop percentage. Review the comparison table for nearby sizes. Final design should still follow local electrical codes, insulation ratings, terminal limits, and manufacturer instructions. Use the result as a planning guide before installation or inspection review. Many residential mistakes come from guessing wire size from breaker rating alone. Length changes the answer. So does low voltage. This calculator combines those factors into one consistent estimate for faster decisions today.
Longer cable runs increase resistance. More resistance causes higher voltage drop and extra heat. That often requires a larger conductor, even when the current stays the same.
Copper usually gives lower resistance and smaller sizes. Aluminum can be cost effective for larger runs. It often needs a larger cross section and correct termination hardware.
Voltage drop is the loss of voltage along the wire. Too much drop can cause dim lights, weak motor starting, and poor appliance performance.
Continuous loads run for long periods. They create more sustained heating. Many designs apply extra allowance so the conductor and protective device operate more safely.
No. It is a planning tool. Final conductor size, insulation type, and breaker selection should match local codes, equipment ratings, and installation conditions.
Grouped cables and hotter spaces reduce how much current a conductor can safely carry. Derating reflects that reduced cooling condition.
Yes. When measured load current is already known, choose current mode. That skips the power conversion step and calculates conductor size directly from amperes.
Breakers are selected from standard ratings. Designers also consider continuous load allowance and conductor protection. That can make the chosen breaker different from the exact calculated current.