Calculator
Fill the fields below, then press Calculate. Fields adapt to your input method.
Formula Used
The core DC resistance model uses conductor resistivity, length, and cross-sectional area: R = ρ · L / A. This calculator accepts ρ in Ω·mm²/m and converts internally to Ω·m.
Temperature adjustment is applied (when enabled) using: RT = Rref · [1 + α · (T − Tref)]. Parallel runs divide total resistance: R / N.
With current I, voltage drop is V = I · R, and power loss is P = I² · R.
How to Use This Calculator
- Enter the conductor length and choose the unit.
- Select one-way or round-trip circuit length.
- Pick a size method: area, diameter, or AWG.
- Select a material preset, or use custom ρ and α.
- Set operating temperature, stranding factor, and parallel runs.
- Optionally add current to estimate drop and heating.
- Press Calculate, then export CSV or PDF.
Example Data Table
Example resistances at 20°C, one-way length 100 m, using preset Al 1350 (ρ = 0.028 Ω·mm²/m), stranding factor 1.00, and one run.
| Length (m) | Area (mm²) | Resistance (Ω) | Resistance (mΩ) |
|---|---|---|---|
| 100 | 2.5 | 1.120000 | 1120.000 |
| 100 | 4 | 0.700000 | 700.000 |
| 100 | 10 | 0.280000 | 280.000 |
| 100 | 16 | 0.175000 | 175.000 |
| 100 | 35 | 0.080000 | 80.000 |
Resistivity and alloy selection
Electrical aluminum grade 1350 typically uses 0.02800 Ω·mm²/m at 20°C, while AAAC 6201 is near 0.03284. Higher resistivity increases I²R loss, so alloy choice matters for feeders. Use the preset when your drawing calls “EC” or “AAAC”, then overwrite ρ only with a datasheet value. Keep the reference temperature consistent with your source table.
Length definition and circuit modeling
Resistance scales linearly with length, so define L carefully. One-way length models a single conductor path; round-trip doubles L for go and return in DC loops. For a 48 V system carrying 30 A, an extra 10 m of round-trip length adds measurable drop. Use kilometers for long runs to reduce entry mistakes, then verify the effective length shown in results.
Sizing by area, diameter, and AWG
Cross-sectional area drives resistance because R = ρL/A. Area in mm² is preferred for power cabling, but diameter is convenient for solid wire and busbar. AWG inputs are converted to diameter using the standard geometric series, then to area. After conversion, the calculator applies a stranding factor, for example 0.98, to reflect packing and air gaps in stranded conductors.
Temperature rise, voltage drop, and losses
Aluminum resistance increases with temperature using R_T = R_ref[1 + α(T − T_ref)]. With α ≈ 0.00403 1/°C, moving from 20°C to 80°C raises resistance about 24%. Voltage drop is V = IR, and heating loss is P = I²R. If current is unknown, leave it blank and focus on Ω or Ω/km for sizing comparisons.
Validation and engineering workflow
Use the example table to sanity check: at 100 m, 16 mm² with ρ = 0.028 gives about 0.175 Ω one-way at 20°C. Compare the per-kilometer figure with catalog data to validate inputs. For parallel runs, divide resistance by N only when runs are equal length and termination. Document assumptions, export CSV, and attach the PDF to design reviews. Also consider connection resistance, especially on lugs and splices, where oxide layers can dominate milliohm budgets. For long runs, check both steady-state and cold-start values, and record the assumed conductor temperature clearly. When verifying on-site field measurements, use four-wire methods to separate lead and contact errors.
FAQs
What resistivity should I use for aluminum?
Use the preset for Al 1350 (0.02800 Ω·mm²/m at 20°C) or AAAC 6201 (0.03284). Replace ρ only when you have a manufacturer datasheet or a tested value at a known reference temperature.
Why does round-trip length matter?
A circuit has a supply path and a return path. For most DC and single‑phase loops, current travels out and back, so effective length is roughly twice the one-way distance, doubling resistance and voltage drop.
How do I choose a stranding factor?
Stranded conductors have small voids and slightly less effective metal area than a perfect solid circle. Values like 0.98 are common for flexible cable. Use 1.00 for solid wire or when your specified area already accounts for stranding.
What temperature should I enter?
Enter the expected conductor operating temperature, not ambient. If you are sizing for code limits, use a conservative value such as 60–90°C depending on insulation class and installation. Keep the reference temperature consistent with the ρ and α you use.
Does the result include AC skin effect?
No. The calculator uses DC resistance with an optional temperature correction. At higher frequencies, skin and proximity effects increase effective resistance. For AC busbars, harmonics, or RF, use an AC resistance model or manufacturer impedance tables.
How should I model parallel runs?
If runs are identical in length, size, and terminations, N parallel conductors share current and reduce resistance by about 1/N. Enter the run count to estimate lower voltage drop and loss. Unequal paths may not split current evenly.