Cable Sizing Calculator
Find the minimum conductor size that keeps a DC string or AC run under its voltage-drop limit, then round up to the next standard cable size, with the resulting drop shown.
Inputs
View resultLive result
Edit inputsMinimum area
1.93mm²
Standard size
2.5mm²
Drop at that size
0.77%
Save or file this result
- Sizes a conductor for voltage drop only: the minimum cross-sectional area that keeps drop under your target limit, then the next standard size up.
- This is not a current-carrying-capacity (CCC) check. You must still confirm the conductor's rating against AS/NZS 3008.1 tables for your install method, grouping and ambient temperature.
- The voltage-drop target is supplied by the user; the tool does not infer which design criterion applies.
How it works
This sizes a conductor for voltage drop only. Rearranging the voltage-drop formula for the minimum cross-sectional area:
A_min = (k × length × current × ρ) ÷ V_drop, where k = 2 for a DC or single-phase two-wire run (active + return) or √3 for three-phase, ρ is resistivity (~0.0175 Ω·mm²/m copper, ~0.0282 aluminium near 20 °C), and V_drop is the allowed drop in volts (drop % × system voltage ÷ 100).- The result is rounded up to the next standard conductor size (1.5, 2.5, 4, 6, 10, 16 mm²…), and the drop that size actually achieves is shown.
Enter the voltage-drop criterion that applies to the actual circuit and project. The tool deliberately does not infer a compliance limit. Treat the result as a first check, not a cable schedule.
Important. This is not a current-carrying-capacity check. A conductor must also carry its load current safely for the install method, cable grouping, insulation and ambient temperature. Confirm the current-carrying capacity against the AS/NZS 3008.1 tables (this tool does not reproduce them), and have a licensed electrician sign off the final design.
Estimates only: for guidance, not a quote or a compliance certificate. Verify against the current AS/NZS standards and a licensed design. The maths runs in your browser. Nothing is sent to Wattbench unless you sign in and deliberately save the result.
Source ledger2 sources
- Standards bodyAS/NZS 3008.1.1:2017 — Standards Australia catalogue
- Standards bodyAS/NZS 5033:2021 — Standards Australia catalogue
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Frequently asked
- Does this size the cable for current-carrying capacity?
- No. It sizes purely for voltage drop. Current-carrying capacity depends on install method, cable grouping, insulation and ambient temperature, and must be checked against the AS/NZS 3008.1 tables. This tool does not reproduce those tables.
- Which resistivity does it use?
- The tool discloses fixed copper and aluminium resistivity inputs in its method. A complete design must instead use the applicable conductor data and AS/NZS 3008.1 tables for the cable, installation method and design conditions.
- Is it free, and is my data stored?
- It is free with no sign-up. The calculation runs in your browser, and nothing is sent to Wattbench unless you sign in and deliberately select Save result.
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