calctricFrom input to answer.
- Open All Tools → Wire Spool. Use only an isolated, de-energized conductor for resistance measurements.
- Choose material, wire size and construction. Enter measured resistance in the labelled unit.
- Enter lead correction and conductor temperature. Choose One wire or Two-wire loop to match the measurement path.
- Read the approximate length and review the reference and meter details.
WORKED EXAMPLE
Estimating a partly used spool
Enter
Use 12 AWG stranded copper, 0.74 Ω, zero lead correction, 20°C and One wire.
Read the result
The estimate is approximately 454.5 ft (138.5 m). A two-wire loop with the same corrected resistance represents half that one-way length when both wires are identical.
Get more from it.
- Lead and contact resistance can be a large share of a short-wire measurement.
- Use conductor temperature rather than assuming room temperature for a hot or cold spool.
Know the limits.
- Nominal DC resistance data and temperature correction give an estimate, not a certified length. Parallel paths, connections and meter resolution affect it.
- The reference includes NEC 2026 Table 8 resistance data for the supported conductors. This is not an ampacity or code-sizing result.
Verify the inputs, applicable local requirements and real conditions. The app is a calculation aid and can contain errors. See our terms and safety disclaimer.
Common questions.
Can I measure an energized circuit?
No. This workflow requires isolated, de-energized conductors and suitable measurement practice.