Cable Size Calculator
Cable Calculator

Cable Calc

Cable size calculation app with volt drop and correction factors.

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Cable Calculation Software

Cable Size Calculator


An easy to use cable size calculator for calculating the minimum required cable sizes 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

The Ultimate Electrical Cable Size Calculator

Unleashing the power of precision, our Electrical Cable Size Calculator is a game-changer for industry professionals. This essential tool provides a seamless way to determine the ideal cable size for any electrical project, ensuring efficiency and safety. With its user-friendly interface, navigating complex calculations has never been easier. Whether you’re a seasoned electrician or a novice DIY enthusiast, this calculator simplifies the process, allowing you to make informed decisions with confidence.


Utilizing advanced algorithms, our calculator considers various factors such as voltage drop, current, and maximum Zs values, delivering results in seconds. Say goodbye to guesswork and hello to accuracy. Empower your projects with the right cable size, saving time, money, and potential headaches down the line. From residential wiring to large-scale industrial installations, this tool is a must-have in your arsenal. Embrace the future of electrical design and installation with our Electrical Cable Size Calculator and take the headache out of cable sizing.

App Reviews

Don’t take our word for it – here’s what some cable calc app users say,

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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Download for Android

Calculating Cable Sizes


Understanding the importance of choosing the right electrical cable size


Selecting the right electrical cable size is crucial for the overall safety and efficiency of any electrical installation. Inadequate cable sizing can lead to voltage drops, increased energy consumption, and potential hazards such as overheating and fire. On the other hand, oversized cables can result in unnecessary expenses and inefficiencies. Therefore, understanding the factors that influence cable size selection is paramount for any electrical project.


The environmental conditions in which the cables will be installed play a significant role in determining the appropriate size. Factors such as temperature, moisture, and mechanical stress can impact the performance and longevity of the cables. Additionally, considering the voltage and current requirements of the electrical system is essential for proper cable sizing.


By taking these factors into account, professionals can ensure that the chosen cable size meets the specific needs of the project.

The basics of electrical cable sizing


Electrical cable sizing is based on the concept of current-carrying capacity and voltage drop. Current-carrying capacity refers to the maximum current that a cable can continuously carry without exceeding its temperature rating. On the other hand, voltage drop is the reduction in voltage that occurs as current flows through the cable. Both of these factors are critical in determining the appropriate size of the cable for a given application.


The American Wire Gauge (AWG) system and the cross-sectional area (CSA) mm² of the conductor are commonly used to specify cable sizes depending on the country. Larger cross-sectional areas result in lower electrical resistance, thereby reducing voltage drop and allowing for higher current-carrying capacity. Understanding these fundamental principles is essential for accurately sizing electrical cables to meet the specific demands of an electrical system.

Common mistakes to avoid when sizing electrical cables


Despite the availability of advanced tools such as the Electrical Cable Size Calculator, several common mistakes can compromise the accuracy and safety of cable sizing. One prevalent error is neglecting to account for voltage drop, which can lead to underperforming electrical systems and potential equipment damage. Additionally, overlooking environmental factors such as temperature and moisture can result in premature cable failures and safety hazards.


Another common pitfall is relying solely on theoretical calculations without considering real-world conditions and system dynamics. Failing to anticipate future load growth and expansion can lead to undersized cables, necessitating costly and disruptive upgrades down the line. By being aware of these common mistakes and leveraging calculation tools like our calculator, professionals can avoid these pitfalls, ensuring that their cable sizing decisions are optimized for safety, performance, and long-term reliability.

Factors to consider when selecting electrical cable size


When selecting the electrical cable size for a particular application, several key factors must be taken into consideration. The first and foremost consideration is the maximum current that the cable will need to carry. This is crucial in preventing overheating and ensuring the safety and reliability of the electrical system. Additionally, the length of the cable run, along with the voltage drop limits, must be carefully evaluated to avoid performance issues.


Environmental conditions, including ambient temperature and exposure to moisture, chemicals, or physical damage, must also be factored into the cable size selection process. It’s imperative to choose cables that are designed to withstand the specific environmental challenges they will encounter. Furthermore, future expansion and load growth should be anticipated to avoid the need for premature cable upgrades.


By carefully evaluating these factors, professionals can make informed decisions when selecting the most suitable cable size for their projects.

The cable size calculator: How it works


Our Electrical Cable Size Calculator harnesses the power of advanced algorithms to streamline the cable sizing process. By inputting key parameters such as voltage, current, ambient temperature, and cable length, the calculator quickly computes the cable size for the given application. Its intuitive interface and real-time calculations empower users to make informed decisions without the need for complex manual calculations.


The calculator takes into account industry standard (UK) correction factors, ensuring that the results align with safety and performance requirements. Its ability to consider multiple variables simultaneously eliminates the guesswork associated with traditional cable sizing methods, providing users with confidence in their electrical design and installation decisions. Whether it’s a simple residential wiring project or a complex industrial installation, our calculator simplifies the process, saving time and resources while enhancing overall project efficiency. Always check and verify the cable calculation results by another means before implementing.

Comparison of different electrical cable size calculators


While there are several electrical cable size calculators available in the market, not all are created equal. When comparing different calculators, it’s essential to consider factors such as the range of input parameters, the accuracy of calculations, and the user interface’s ease of use. Our Electrical Cable Size Calculator stands out for its comprehensive approach, accommodating a wide range of input variables and delivering instant result.


Additionally, the ability to customize calculations based on specific installation conditions and project requirements sets our calculator apart from generic alternatives. Its seamless integration of industry guides (BS 7671) and best practices ensures that the recommended cable sizes align with safety and performance expectations. By choosing a reliable and feature-rich calculator like ours, professionals can optimize their cable sizing processes and elevate the overall quality of their electrical design and installation work. Always check and verify the cable calculation results by another means before implementing.

Cable Calc

iOS | Android | Web
  • Save the calculation results as a PDF
  • Includes correction factors
  • Includes various installation methods
  • Cable Sizes in mm²

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