Cablerate sizes cables the way a designer works on paper. It goes from the load to the protective device, through every correction factor, to the smallest cable that passes, then checks voltage drop. Every step is shown, so you can see exactly why a 6mm² cable became a 10mm².

Built for electricians, apprentices, electrical designers and estimators working to BS 7671 (18th Edition). Cablerate works fully offline, with no account, no ads and no permissions.

SIZE A CABLE IN FIVE CLEAR STAGES
- Load: enter the design current, or convert from W, kW or kVA for single-phase and three-phase circuits, with power factor.
- Protection: choose an MCB/RCBO or a BS 88, BS 1361, BS 1362 or BS 3036 fuse from standard ratings, with an Ib ≤ In check.
- Route: pick the cable type and reference installation method from illustrated cards.
- Environment: ambient temperature, grouping, thermal insulation and rewireable fuse factors are applied for you.
- Run: set the cable length and voltage drop limit, including drop already used upstream.

SEE THE DERATING TRACE
The derating ladder shows the required current building up as each factor is applied, and which cable size passes first. A written trace lists every formula, value and regulation reference, and can be copied as text.

VOLTAGE DROP CHECKED PROPERLY
Cablerate checks voltage drop against 3% or 5% limits, 6% or 8% for private supplies, or a limit you set. It upsizes the cable when drop is too high and shows the maximum run length for the selected size. Ring final circuits and grouped circuits not liable to simultaneous overload are supported.

CHECK AN EXISTING CABLE
For additions and alterations, enter an installed cable and its conditions to find the largest protective device it can take and its maximum run length.

ORGANISE WHOLE JOBS
- Build a supply tree of sub-mains and final circuits, so upstream voltage drop carries through to every circuit.
- View the whole job as a cable schedule.
- Compare up to three what-if alternates side by side and adopt the one you want.
- Issue revisions (Rev A, B, C) and compare any revision with the current design.
- Use Quick Size for one-off calculations, with recent history kept.

EXPORT AND BACK UP
Create PDF design sheets and full job reports, export the cable schedule as CSV, and back up all your data to a single file you control.

CABLES COVERED
Flat twin and earth, single-core and multicore thermoplastic cables, and armoured thermoplastic and XLPE (SWA) cables, using current ratings and correction factors from BS 7671 Appendix 4.

PRIVATE AND OFFLINE
No internet access, no account, no ads and no analytics. Everything you enter stays on your device.

Cablerate also includes a reference library of correction factor tables, installation methods, formulas and a glossary, plus light and dark themes.

Please note: Cablerate is a design aid. Results should be checked by a competent person against the current edition of BS 7671 before installation.