Cable size calculator to calculate the required cable sizes for various cables types, installation methods, correction factors and protective devices, BS7671 18th edition version.

Calculates cable size, r1+r2, volt drop %, and determines what the expected Zs value will be.

Carry out on the spot instant cable calculations, great for electrical surveys, condition reports, circuit design and cable sizing on the go.

- Print, Save, Email & Share the cable calculation results PDF (from the print function)
- Verification checks and helpful hints
- Support for manufacturer specific BS EN 60947-2
(max Zs) MCCB's & ACB's
- Support for RCD's in TT Earthing Systems

This cable calculator also checks the volt drop %, max Zs, R1+R2 and applies the relevant correction factors from an easy to use selection list of options.

How to share or email the cable calc results PDF file:
1) On the Results screen tap "Print".
2) Expand the displayed image (preview window is then displayed).
4) Tap the share icon to show your device's share and save options.

Calculate circuit cable sizes for final circuits, distribution circuits and sub main electrical supplies.

This cable sizing app can also be used to check the electrical cable ratings for different electrical installation methods to ensure existing cables or wires are compliant on existing installations for an Electrical Installation Condition Report (EICR) including volt drop and Max Zs.

You can also use cable calc to check existing installed cable sizes and circuits to check for compliance and to confirm the correct cable size for the type of cable, installation method and length of circuit has been selected and installed correctly.

This cable calculator also takes into account and applies the following factors for it's cable size calculation formula:
+ Volt drop
+ Correction factors
+ Maximum disconnection times
+ Length of circuit
+ Various installation methods
+ Various cable types
+ Tabulated Current
+ Maximum Zs Values
+ Calculates Zs
+ Calculates r1+r2
+ Calculates volt drop %
+ Adjusted required minimum required cable ratings
+ Calculates cable size

Correction Factors:
Cg - Grouping
Ca - Ambient air temperature
Ca - Ambient ground temperature (if cable is buried
or in a duct)
Ci - Thermal insulation
Cf - BS 3036 semi-enclosed fuses (rewire-able)

Mobile cable sizing software for iPhone and iPad.

You may also like our new 'Pro Certs' app for iPad, produce professional electrical installation certificates and condition reports on the go.

Check out our collection of electrical apps for iOS

What’s New

Version 1.3.4

June 2020: Back-end improvements and reduced app download file size.

Ratings and Reviews

3.4 out of 5
5 Ratings

5 Ratings

Dj Edison ,

Great App

I personally have not had a problem with this app. It’s a really useful app for those who want to check cable requirements on the fly.

Developer Response ,

Thank you for your feedback.

Dayo17 ,


Great fast calculating tool very accurate

dd sparky ,

D Evans

Worst cable calc app, tried getting the cable size for a 209amp circuit would not do it so I tried a smaller circuit and it recommended 16mm T&E for a 25 amp supply covered by a 32amp rcbo

Developer Response ,

Other parameters also apply to a cable calculation (other than just the rating) such as the Ze, max Zs, volt drop, cable resistance and installation methods. A high Ze or long circuit will increase the required cable size. Correction factors also have an effect on the cable size. Can you send your calculation requirements to


Pro Certs Software Ltd
6.7 MB

Requires iOS 10.0 or later. Compatible with iPhone, iPad and iPod touch.



Age Rating


  • Family Sharing

    Up to six family members will be able to use this app with Family Sharing enabled.

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