Cable Size Calculator
Cable Calculator

Cable Calc

Cable size calculation app with volt drop and correction factors.

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Cable Calculation Software



An easy to use cable size calculator to calculate the minimum required cable size for various cable types, protective devices, installation methods and correction factors, also calculates voltage drop, R1+R2 and Ze, based on BS 7671 the UK IET wiring regulations

Do you ever need to carry out a quick on-site cable size calculation? If so, this is where this cable calculator becomes handy, a pocket sized cable calculator app for your mobile device.

- Calculate a cable size in two easy steps with instant results!


  • Cable Size Calculation
  • Maximum Zs
  • Voltage Drop Calculation
  • Tabulated Current (It)
  • Expected Zs
  • Print or Save The Results
  • Expected R1+R2
  • Digitally Sign & Approve

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Cable Size Calculator

Cable Size Calculations


Carry out instant cable calculations, great for electrical surveys, condition reports, circuit design and cable sizing on the go. This cable size calculator has been designed to make it as easy as possible, calculate a cable size in two simple steps.



Input your circuit design parameters:

  • Design Current
  • Length of Circuit
  • Supply Voltage
  • Source Ze or Zdb


Select your design options:

  • Voltage Drop %
  • Earthing Type
  • Protective Device Type
  • Device Rating
  • Cable Type
  • Max Disconnection Time

Correction Factors


In step 2 we apply and relevant correction factors. For BS 3036 fuses a correction factor is automatically applied if a BS 3036 protective device is selected.



Select from the available options:

  • Installation Method
  • Ambient Temperature
  • Grouping
  • Surrounded by Thermal Insulation


Then tap the calculate button to display the results.


  • Cg : Grouping
  • Ca : Ambient air temperature
  • Ca : Ambient ground temperature
  • Ci : Thermal insulation
  • Cc : BS 3036 semi-enclosed fuse
Cable Calc Software
Step 2
BS 7671 Cable Calculator
Cable Size Calculator

Cable Calculation


The cable calculation results screen displays your circuit design data, selected options, cable size and other related calculation results.


Cable Size Calculator Calculations:

  • It : Tabulated current
  • R1+R2 : Circuit expected R1+R2 value
  • Zs : Circuit expected Zs value
  • Max Zs : Calculated max Zs values for 0.2s, 0.4s & 5s (80% + 100% values)
  • Vd : Calculated voltage drop %
  • CF : Total applied correction factor value
  • Minimum required cable size (mm²)

Saves Time


Calculating cable sizes need not be daunting, let the cable calc app do it for you.


Other Features

Print cable calculator results
Verification and validation checks
Support for manufacturer specific MCCB’s & ACB’s (max Zs)
Support for RCD’s in TT Earthing Systems

  • Quick and easy
  • Saves time
  • Print the results
  • Digitally sign
Cable Calculation Software
Print the results



What are correction factors?

Correction factors are multipliers applied to cable sizing calculations for specific circumstances.

Correction factors include:
  • Cg Grouping
  • Ca Ambient air temperature
  • Ca Ambient ground temperature
  • Ci Thermal insulation
  • Cc BS 3036 semi-enclosed fuses

What is Zdb?

Zdb (ZDB) is the term generally used to refer to the earth loop impedance at a distribution board.

What is design current?

The circuit design current is the minimum amount of current the circuit needs to be able to sustain in normal use.

To calculate the design current or maximum demand check out our Diversity / Maximum Demand Calculator App.

What is Voltage drop?

Voltage drop is the amount of volts lost due to the resistance of a cable, the longer the cable is the higher the volt drop will be.

This is also true for varying cable sizes, the smaller the cable the higher the voltage drop will be, hence for long circuits a larger cable might be required to satisfy the maximum permitted voltage drop.

Volt Drop Calculation


This cable calculator will also calculate and apply a voltage drop calculation as part of the cable sizing calculation process. Volt drop is generally measured in mV (millivolts) or as a percent (%), 1 millivolt is one thousandth of a volt.


If a cable calculation fails the Volt drop maximum but passes all other requirements such as Max Zs, Current Carrying Capacity etc. then you will be prompted with a message “Volt Drop Compliance Failed, try next cable size up?” to select the next larger cable size to then try the full calculation again until all of the requirements are met before selecting the most suitable cable size.


If you only need to carry out a Voltage Drop Calculation and not a Cable Size Calculation you can use our free Voltage Drop Calculator.

Volt Drop Calculation

Demo video may show an older version of the app

Cable Calc


Calculate cable sizes for a variety of  cable types and installation methods.

  • Print the results
  • Calculate Volt Drop
  • Calculate Estimated Zs and R1+R2
  • Calculate Cable Size
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