Is this calculator free to use?

Yes. The voltage drop calculator is free and needs no sign-up. It runs entirely in your browser.

Does it support both DC and AC runs?

It works out two-wire DC or single-phase AC voltage drop from the values entered. It does not infer a permitted limit or replace a complete cable design.

Engineering Tool

Solar Cable Voltage Drop Calculator

Work out voltage drop on a DC string or single-phase AC run from the entered length, current, conductor size, voltage and material.

Sources listedReviewed July 2026Our methodology

Inputs

View result

Run length (one-way)Distance one way; the return conductor is included.

Length unit

Operating current

Conductor cross-sectionUse the conductor cross-section for the actual run.

System voltageUse the operating or design voltage for the circuit.

Conductor material

Live result

Edit inputs

Voltage drop

0.88V

Drop percentage

0.22%

Compare this result with the criteria applicable to the actual circuit and installation. Wattbench does not infer a permitted limit from these inputs.

Save or file this result

Key takeaways

Works out voltage drop on a DC string or single-phase AC run.
Uses run length, current, conductor size, voltage and material as inputs.
Returns the drop in volts and as a percentage without inferring the applicable design limit.

How it works

For a two-wire DC string or single-phase AC run, voltage drop is:

V drop = (2 × length × current × ρ) ÷ area, where the factor of 2 covers the active and return conductors, and ρ is conductor resistivity (~0.0175 Ω·mm²/m for copper, ~0.0282 for aluminium, near 20 °C).
Drop % = V drop ÷ system voltage × 100.

Real designs use the applicable temperature, installation method, conductor data and circuit criteria. Three-phase circuits also use a different factor. This tool reports the arithmetic result without inventing a pass limit; it is a first check, not a substitute for a licensed electrician's cable sizing.

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

Continue this work

AS/NZS 3008.1Standard AS/NZS 5033Standard

Did this help you move the job forward?

Good to know

Frequently asked

Is this calculator free to use?: Yes. The voltage drop calculator is free and needs no sign-up. It runs entirely in your browser.
Is my data stored or sent anywhere?: The calculation runs in your browser. Nothing is sent to Wattbench unless you sign in and deliberately select Save result.
Does it support both DC and AC runs?: It works out two-wire DC or single-phase AC voltage drop from the values entered. It does not infer a permitted limit or replace a complete cable design.

Keep calculating

More tools

Identification Tool

Single or Three-Phase Supply Check

Use visible main-switch or meter clues to identify a likely single- or three-phase supply without opening the switchboard.

Likely supply · visible clue · safety check

Supply Worksheet

Three-Phase Load Balance Worksheet

Compare entered phase currents, identify the highest and lowest phase, and quantify the spread without asserting a compliance limit.

Average current · phase spread · highest phase

Grid Worksheet

AC Voltage Rise Worksheet

Compare two entered voltage readings and document the rise in volts and percentage without applying a compliance verdict.

Voltage rise · rise percentage · recorded headroom