Kabelquerschnitt-Rechner
Planung von Cu oder Al aus Strom (oder Leistung), Spannung, einfacher Leitungslänge und Spannungsfall — mit vereinfachter 75°C-Ampacity. Nur Orientierung.
Bemessungsstrom. Leer für Schätzung aus Watt.
Oder Strom aus Leistung
Real power (watts).
Für %-Spannungsfall. Zwei-Leiter-Einphase.
Used only when deriving amps from watts. Blank = 1.
Quelle bis Verbraucher.
Planning limit — many designs use ~3% for branch circuits and ~5% for feeders (check your standard).
Table of Contents
Nur Planungshilfe
Branch and feeder conductors must carry current without overheating (ampacity) and often must limit voltage drop so equipment sees a stable voltage at the load.
This tool walks a consolidated ampacity table (75°C, simplified “not more than three CCC in raceway/cable”) and a single-phase, two-conductor voltage-drop estimate using resistance per thousand feet.
You can type amps directly or derive them from watts, voltage, phase, and power factor — same pattern as our breaker calculator.
Ambient temperature, conduit fill, parallel runs, harmonics, NEC exceptions, terminal ratings, and local amendments are not modeled. Use the output as a conversation starter with your AHJ or engineer — not as a final specification.
What is calculated
Voltage drop (single-phase, 2-wire)
V_drop ≈ 2 × I × (L_ft ÷ 1,000) × R_Ω/kft
I is amperes, L_ft is one-way length in feet, R is conductor resistance in ohms per 1000 ft at 75°C (material-specific). Percent drop = 100 × V_drop ÷ V_circuit.
Ampacity
Each row includes a maximum ampacity for copper and aluminum at 75°C under simplified bundling assumptions. The suggested size is the smallest listed conductor that meets both I ≤ ampacity and percent drop ≤ your limit.
Excerpt — common smaller sizes (75°C, simplified)
| Size | A (Cu) | A (Al) | Notes |
|---|---|---|---|
| 14 AWG | 15 | — | Al not used at this step in table |
| 12 AWG | 20 | 15 | Typical small-branch range |
| 10 AWG | 30 | 25 | |
| 8 AWG | 40 | 35 | |
| 6 AWG | 55 | 40 |
Examples
20 A, 120 V, 75 ft, copper, 3% drop
Often lands on 12 AWG for ampacity; the calculator checks drop on each step and keeps the smallest that satisfies both.
Long 120 V run
Voltage drop dominates — you may land several sizes larger than ampacity alone would require.
Aluminum feeder
Lower ampacity per gauge and higher resistance mean aluminum often requires a larger conductor than copper for the same job.
Three-phase loads
Current-from-power supports balanced three-phase using line-to-line voltage, but the voltage-drop model here remains single-phase pair — use engineering software for long three-phase runs.
FAQ
Tables vary by code edition, conductor type (THHN/XHHW), duty, dirt, and rooftop exposure. We use a single simplified 75°C column for planning.
If the load current field has a valid positive value, it is used and the power fields are ignored until you clear amps.
No. It sizes a current-carrying phase/neutral pair for ampacity and drop. Equipment grounding conductors follow separate rules.
Branch-circuit OCPD limits for small conductors are not enforced here — pair this tool with proper breaker/fuse sizing and code limits.
We show approximate mm² next to each AWG/kcmil. Final metric projects should use manufacturer data and local wiring rules.
Use the Circuit Breaker Size Calculator for OCPD planning and our electrical suite (watts, amps, volts) to refine load current before sizing wire.