20 amp copper branch circuit
Common household branch-circuit lookup.
12 AWG copperCommon minimum conductorwire calculator
Wire Calculator
Wire size depends on ampacity and conditions of use; long runs, conduit fill, temperature, terminals, and equipment instructions can require different sizing.
Inputs
Results
Immediate estimateCommon minimum conductor12 AWG copperLimited 60C-style planning lookup; confirm the actual code path.
Circuit rating20 A
MaterialCopper
Length50 ft
Voltage dropNot estimated
Acknowledge the limitations before relying on this as a planning lookup.
Conductor size depends on insulation rating, terminals, cable type, ambient temperature, conduit fill, bundling, equipment rules, and local code.
Diagram
Wire lookup
Circuit rating and conductor material select a limited common-size row.
- Breaker amps
- Material
- Run length
How this calculator works
Select circuit rating, conductor material, and run length to get a cautious common-size lookup and voltage-drop warning.
Lookup scope
The MVP maps selected common residential circuit ratings to common copper or aluminum conductor sizes.
No extrapolation
Unsupported combinations are labeled unsupported rather than guessed.
Electrical safety
The calculator is intentionally warning-heavy because electrical work can create fire, shock, and inspection risks.
Lookup
match conductor material and circuit amp rating to supported sizeLength flag
flag one-way runs over 100 ft for voltage-drop reviewAssumptions
- Lookup scope: Common copper and aluminum planning sizes for selected residential circuit ratings only.
- Not checked: Voltage drop, grounding conductors, service entrance rules, temperature correction, conduit fill, and equipment-specific instructions.
Worked examples
Long 50 amp run
Shows voltage-drop caution.
6 AWG copperCommon minimum conductorFAQ
Is this electrical advice?
No. It is a planning lookup. Confirm the adopted NEC edition, local amendments, equipment labels, and permit requirements.
Does it calculate voltage drop?
No. It flags longer one-way runs so voltage drop can be checked separately.
Does it size ground wires or conduit?
No. Grounding conductors, conduit fill, derating, and service rules are outside this MVP.
Sources and review
- National Electrical Code, NFPA. Accessed 2026-07-16.
Reviewed 2026-07-16. Planning estimates only; confirm project-specific requirements.