Calculate the correct cable size for your electrical installation based on BS7671 and IEC 60364-5-52 standards
Calculate voltage drop, current capacity, and recommended cable sizes instantly
A cable size calculator is an essential tool for electrical professionals that determines the appropriate cable cross-sectional area (measured in mm²) required for safe and efficient electrical installations. Our calculator considers multiple factors including load current, cable length, voltage drop limitations, installation method, and conductor material to recommend the optimal cable size.
Whether you're working on residential, commercial, or industrial projects, proper cable sizing is critical for safety, compliance, and cost-effectiveness. Undersized cables can overheat and pose fire risks, while oversized cables waste money and installation space.
Full compliance with British Standard BS7671 (IET Wiring Regulations) for UK electrical installations
International standard calculations for global electrical projects
Automatic calculation of voltage drop percentage with 3% compliance limit
Comprehensive current carrying capacity calculations for safe cable selection
Calculations for both copper and aluminum conductors with appropriate derating
Support for both single-phase (230V) and three-phase (415V) systems
Clipped direct, conduit, trunking, cable tray, free air, and underground installations
Enter load in Amps or kilowatts (kW) for maximum convenience
The calculator will instantly provide the recommended minimum cable size, calculated current, maximum current rating, voltage drop in volts, and voltage drop percentage.
BS7671, also known as the IET Wiring Regulations, is the national standard in the United Kingdom for electrical installation and safety. It covers the design, erection, and verification of electrical installations to protect persons, property, and livestock from electric shock, fire, and burns. The current edition is BS7671:2018+A2:2022.
IEC 60364-5-52 is the international standard for selection and erection of electrical equipment - wiring systems. It's widely used across Europe and many other countries. This standard provides guidelines for cable selection, current-carrying capacity, and voltage drop calculations.
Both BS7671 and IEC 60364-5-52 specify maximum voltage drop limits:
The cable must be able to carry the full load current continuously without overheating. Current ratings depend on conductor material (copper has higher capacity than aluminum), cable size, insulation type, and installation method.
As current flows through a cable, resistance causes voltage drop. Longer cables and higher currents result in greater voltage drop. The voltage at the load end must remain within acceptable limits (typically 3-5% of supply voltage).
How a cable is installed significantly affects its ability to dissipate heat:
Copper and aluminum are the two primary conductor materials:
Standard cable cross-sectional areas (in mm²) available in this calculator:
Important: This calculator provides guidance for cable sizing based on standard conditions and typical installation scenarios. Always ensure that:
This calculator is provided as a design tool and guide only. It should not replace professional engineering judgment or official electrical design documentation. Always consult with a qualified electrician or electrical engineer for critical installations.
Cable size refers to the cross-sectional area of the conductor (measured in mm²), while current rating is the maximum current the cable can safely carry continuously. Larger cable sizes have higher current ratings. The current rating depends on both the cable size and the installation method.
Installation method affects how well a cable can dissipate heat. Cables in free air cool better than cables buried in insulation. Poor heat dissipation reduces the safe current carrying capacity, requiring larger cable sizes.
Yes, using a larger cable than calculated is safe and may be beneficial. It provides additional safety margin, reduces voltage drop further, and allows for future load increases. However, it also increases material and installation costs.
If voltage drop exceeds 3%, you should use a larger cable size. High voltage drop can cause poor performance of equipment, dimming lights, motor problems, and inefficiency. The calculator will recommend the next larger size to bring voltage drop within limits.
When multiple cables are grouped together (in the same conduit or cable tray), they cannot dissipate heat as effectively. This requires applying grouping factors (derating factors) to reduce the effective current rating. For precise calculations with grouped cables, consult BS7671 or IEC 60364-5-52 for appropriate derating factors.
Power factor depends on the load type:
When in doubt, use 0.8 as a conservative estimate.
This calculator is designed for AC circuits (single-phase and three-phase). DC circuits have different voltage drop calculations and don't use power factor. For DC applications, consult DC-specific cable sizing tools or standards.
Cable Size Calculator is a free, professional-grade tool designed to help electrical professionals, engineers, contractors, and students accurately determine cable sizes for electrical installations. Our calculator implements the latest standards and provides instant, reliable results for safe and compliant electrical design.
Whether you're designing residential wiring, commercial electrical systems, or industrial power distribution, our calculator provides the accuracy and reliability you need for professional electrical design work.