Guide

Wire Sizing Glossary (AWG, SWG, mm²) for UK Work

Plain-English definitions for the wire terms most often seen in UK quoting, design, conversion, and handover discussions.

Overview

Use this glossary to keep technical language consistent across UK design notes, quotes, and handover documents when mixed unit systems appear.

AWG: American Wire Gauge. Common on imported product data sheets. In UK workflows, AWG is typically converted into mm² before final sizing decisions.

SWG: Standard Wire Gauge. Legacy UK gauge notation still seen in historical documentation and retrofit contexts.

mm² (square millimetres): Metric cross-sectional area and the primary unit used for modern UK conductor sizing and communication.

Cross-sectional area (CSA): The effective conductor area used in resistance and voltage-drop calculations.

Voltage drop: The reduction in voltage along a cable run under load, usually reported as volts and as a percentage of system voltage.

Resistivity (rho): A material property that influences resistance. Copper and aluminium differ, so assumptions must be explicit.

Resistance (R): Opposition to current flow through a conductor, driven by material, length, area, and temperature assumptions.

Power loss (I²R): Heat-related loss associated with conductor resistance and current.

BS 7671 framing: Using current UK wiring-regulation context to guide verification without claiming calculator outputs are compliance results.

One-way length: Route length from source to load used as the input convention in these calculators.

Estimator output: A planning-oriented result designed to support decisions, not replace full design verification.

Versioned formula: A calculation definition with an explicit version so reported results can be traced to a specific implementation.