Feeder Size Calculator

Electricity is an essential part of our modern lives, powering everything from our homes to industries. When designing electrical circuits, it’s crucial to determine the appropriate feeder size to ensure safety and efficiency. Our Feeder Size Calculator simplifies this process by providing a quick and accurate calculation based on the input of current and voltage.

Feeder Size Formula: To calculate the feeder size, we use the following formula:

The feeder size (FS) is calculated using the formula: FS = (2 * ρ * I) / (V * PF)


  • FS is the feeder size in circular mils.
  • ρ (rho) is the resistivity of the material (assumed to be 1.724e-8 ohm-meters for copper).
  • I is the current in amperes.
  • V is the voltage in volts.
  • PF is the power factor.

How to Use:

  1. Enter the value of the current in amperes.
  2. Input the voltage in volts.
  3. Click the “Calculate” button.
  4. The feeder size will be displayed instantly.

Example: Let’s say we have a circuit with a current of 50 amperes and a voltage of 120 volts. Using our Feeder Size Calculator, we find:

Feeder Size = (2 * 1.724e-8 * 50) / (120 * 0.8) ≈ 0.00014333 circular mils


  1. What is a feeder size?
    • The feeder size refers to the diameter or cross-sectional area of the conductor used in an electrical circuit.
  2. Why is feeder sizing important?
    • Proper feeder sizing ensures that the electrical circuit can handle the current without overheating and causing hazards.
  3. What is power factor?
    • Power factor is the ratio of real power to apparent power in an electrical circuit, indicating the efficiency of power usage.
    • The standard power factor for many circuits is typically assumed to be 0.8.
    • Power factor correction may be necessary for circuits with low power factors to improve efficiency.
  4. What is resistivity?
    • Resistivity is the inherent property of a material that determines its resistance to electrical flow.
    • It is usually measured in ohm-meters.
  5. Can this calculator be used for both AC and DC circuits?
    • Yes, the Feeder Size Calculator can be used for both alternating current (AC) and direct current (DC) circuits.
    • Ensure to input the appropriate values for current and voltage depending on the type of circuit.
  6. What units are used for the result?
    • The result is displayed in circular mils.
  7. What if my power factor differs from 0.8?
    • You can input the specific power factor value in the calculation for accurate results.
  8. Is this calculator suitable for all types of conductors?
    • Yes, this calculator provides results for conductors made of materials with known resistivity, such as copper or aluminum.
  9. How accurate are the results?
    • The results provided by the calculator are accurate for the given inputs and assumptions.
  10. Can I use this calculator for high-voltage circuits?
    • Yes, the Feeder Size Calculator can be used for circuits of varying voltages, including high-voltage applications.

Conclusion: The Feeder Size Calculator simplifies the process of determining the appropriate feeder size for electrical circuits. By inputting the current and voltage values, users can quickly obtain the required feeder size, ensuring safe and efficient electrical installations.