Best Cable Sizing App 2026 — Top Picks Compared

Cable sizing to BS 7671 involves multiple variables: design current, correction factors for ambient temperature (Ca), grouping (Cg), thermal insulation (Ci), and semi-enclosed fuses (Cf), reference installation methods, tabulated current-carrying capacities, and voltage drop limits. Getting any variable wrong can result in an undersised cable that overheats under load or an oversised cable that wastes money.

A good cable sizing app automates these calculations, references the correct BS 7671 Appendix 4 tables, applies all correction factors, and verifies voltage drop is within the permitted limits (typically 3% for lighting and 5% for other circuits on a consumer installation). It should also account for the reference installation method and allow you to check correction factors for your specific installation conditions.

Elec-Mate — All-in-one platform with 70+ calculators including cable sizing, plus certificates, AI tools, training, and business management. References BS 7671:2018+A4:2026. From £6.99/month.

Cable Calc — Free standalone cable sizing calculator. Performs BS 7671-compliant cable sizing with correction factors and voltage drop. Works offline. No other features beyond cable sizing.

Voltimum Cable Sizing Tool — Free web-based cable sizing tool from the electrical industry platform. Performs basic cable sizing with correction factors. Requires an internet connection. Limited reference method options.

Hager Specs — Free app from Hager that includes cable sizing along with product specification tools. BS 7671-compliant cable sizing with voltage drop. Works offline. Naturally orientated towards Hager products.

50+ Calculators — Not Just Cable Sizing

Elec-Mate includes cable sizing plus maximum demand, voltage drop, Zs verification, disconnection times, conduit fill, trunking fill, diversity…

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All four apps claim BS 7671 compliance for cable sizing, but the depth varies significantly. Elec-Mate references BS 7671:2018+A4:2026 — the latest version including Amendment 4 issued in July 2024. This matters because A4:2026 introduced changes relevant to certain installation types.

Free tools may not update as promptly when amendments are published. Before relying on any calculator for a live installation, verify it references the current edition and amendment of BS 7671. Elec-Mate displays the regulation edition and table references within each calculator so you can confirm compliance.

Beyond cable sizing, Elec-Mate includes calculators for voltage drop verification, cable sizing to Appendix 4, maximum demand, diversity factors, earth fault loop impedance, prospective fault current, and disconnection time verification. None of the other three apps offer this breadth of calculation.

Cable Calc, Voltimum, and Hager Specs are useful free tools that do one thing: cable sizing. If cable sizing is the only calculation you need and you want it at no cost, any of these tools will serve.

But cable sizing is rarely the only calculation an electrician needs on site. You also need maximum demand to size the supply, Zs values to verify disconnection times, conduit fill rates when planning containment, and voltage drop checks for long runs. Elec-Mate provides all of these in a single app.

Cable Sizing That Flows Into Your Certificates

Size a cable in the calculator, then tap to insert the result directly into your EIC or Minor Works certificate. No re-typing, no copying between apps.

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More importantly, Elec-Mate integrates calculations with certificates. Size a cable, then insert the result directly into your EIC or Minor Works form. No re-typing, no copying between apps. This integration is unique to Elec-Mate and eliminates a common source of transcription errors.