Cable Size Calculator

Choosing the right cable size is critical for ensuring the safety, efficiency, and longevity of any electrical system. Whether you’re planning a home wiring project, setting up an industrial machine, or configuring a solar panel system, under-sizing cables can lead to excessive voltage drop, overheating, or energy loss.

Our Cable Size Calculator simplifies the process by helping you determine the appropriate cross-sectional area (in mm²) for your wiring, based on key parameters like current, voltage, cable length, and material. With just a few inputs, this tool gives you a quick and accurate recommendation—plus details on expected voltage drop and power loss.

How to Use the Cable Size Calculator (Step-by-Step)

  1. Enter the Current (Amperes):
    Input the electrical current that will flow through the cable. This is usually listed on your equipment’s rating label.
  2. Specify the Cable Length (Meters):
    Provide the one-way distance between the power source and the electrical device. For installations where current flows to and from (like DC systems), the calculator factors in round-trip length.
  3. Input the System Voltage (Volts):
    Enter the operating voltage of your system (e.g., 230V for single-phase or 400V for three-phase).
  4. Select the Cable Material:
    Choose between Copper or Aluminum. Copper is more conductive, so thinner cables may suffice.
  5. Set the Allowable Voltage Drop (%):
    Voltage drop is the reduction in voltage as current flows through the cable. Set the max percentage you’re willing to tolerate (3% is common for most systems).
  6. Click “Calculate”:
    The tool will output:
    • Recommended cable size in mm²
    • Actual voltage drop (V and %)
    • Power loss in watts
  7. Click “Reset” to clear inputs and start over.

Example Use Case: Residential Water Pump Installation

Imagine you’re wiring a 1.5 HP water pump that draws 12A from a 230V supply, and it’s located 40 meters from the breaker box. You’re using copper wire and want to keep voltage drop within 3%.

Input:

  • Current: 12
  • Length: 40
  • Voltage: 230
  • Material: Copper
  • Voltage Drop: 3

Result:

  • Recommended Cable Size: 4 mm²
  • Actual Voltage Drop: ~2.81V (~1.22%)
  • Power Loss: ~5.7 Watts

You now know that 4 mm² copper wire is sufficient, keeping losses well below the 3% threshold.

Why Cable Sizing Matters

🔥 Safety

Improper cable sizing can cause overheating and even fires due to excessive resistance.

⚡ Performance

Voltage drops can lead to malfunctioning equipment, dim lights, or slow motors.

💸 Efficiency

Oversized cables waste money; undersized cables waste energy. Our calculator finds the balance.

🛠️ Regulation Compliance

Many electrical codes require voltage drop to be within specific limits—usually 3–5%.

Applications & Use Cases

  • Residential wiring (e.g., HVAC, water heaters)
  • Solar panel installations
  • EV chargers
  • Marine and RV electrical systems
  • Industrial motors
  • LED lighting circuits
  • Off-grid battery banks

Frequently Asked Questions (FAQs)

1. What is voltage drop?

Voltage drop refers to the reduction in voltage as electrical current travels through a wire due to resistance.

2. Why is copper better than aluminum for cables?

Copper has lower resistivity, meaning it conducts electricity more efficiently. It’s also more durable but more expensive.

3. Is 3% voltage drop always acceptable?

3% is a common rule of thumb for branch circuits. For sensitive equipment or long-distance runs, even lower drops may be preferred.

4. Can I use this calculator for AC and DC systems?

Yes. The formula applies to both as long as you use the correct input values and cable length (round-trip for DC).

5. How is power loss calculated?

Power loss (watts) is calculated using the formula: P = I² × R, where I = current and R = resistance of the cable.

6. What is resistivity?

Resistivity is a material property that describes how strongly it resists current flow. It’s measured in Ohm-mm²/m.

7. Should I always round up to the next standard size?

Yes. The calculator automatically rounds up to the nearest standard cable size to meet or exceed your voltage drop target.

8. Can I use this tool for underground cables?

Yes, but note that environmental conditions (e.g., temperature, soil type) can affect capacity. Consult local codes.

9. What happens if I use a smaller cable than recommended?

The wire may overheat, devices may malfunction, and it could lead to long-term damage or fire hazards.

10. Are thicker cables always better?

Not necessarily. They are heavier, more expensive, and harder to install. Use the right size—not just the biggest.

11. Does this account for cable insulation type?

No, this calculator assumes typical installation. For high-temp or buried cables, consult manufacturer specs.

12. What if my calculated size isn’t listed as a standard?

The tool picks the next higher standard size to ensure safe operation and minimal voltage drop.

13. Is this calculator accurate for 3-phase systems?

While the tool simplifies for general use, single-phase assumptions dominate. For precise 3-phase sizing, consult an engineer.

14. Why is aluminum wiring still used?

Aluminum is cheaper and lighter than copper, making it viable for large runs (like utility lines), despite needing larger sizes.

15. What if my voltage drop exceeds the limit?

Use a larger cable, reduce load current, or shorten the cable distance.

16. Can this be used in marine or RV systems?

Yes. For mobile and off-grid systems, voltage drop is critical due to lower voltage and long cable runs.

17. How does temperature affect cable size?

Higher temperatures increase resistance. This calculator uses standard conditions; derating may be needed for hot environments.

18. What’s the max cable size this tool handles?

Up to 630 mm²—suitable for very high current applications.

19. Is there a safety factor included in the results?

Yes. By rounding up to the next standard size, the calculator inherently builds in a safety buffer.

20. Should I consult a professional before installing?

Always. This tool provides guidance, but a licensed electrician should approve and verify final installations.

Final Thoughts

This Cable Size Calculator is a practical tool for electricians, engineers, DIYers, and system designers looking to ensure safe and efficient electrical systems. Whether you’re installing a solar array or running power to a garage, getting cable size right prevents costly and dangerous mistakes.

Bookmark this tool, use it often, and share it with your team or clients for smarter electrical planning.