Cable Calc 4+

BS 7671 Cable Size Calculator

Pro Certs Software Ltd

Designed for iPad

    • 2.5 • 10 Ratings
    • £5.99



Cable calculator for calculating cable size, voltage drop, R1+R2 and Zs.

An easy to use cable calculator to calculate cable sizes for various types of cables, installation methods, correction factors and protective devices.

Calculates cable size, R1+R2, voltage drop and expected Zs in two simple steps.

Carry out instant cable size calculation on the go, great for electrical surveys, EICR reports or designing new circuits.

- 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

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 the cable size for final circuits, distribution circuits and sub-main supplies.
You can also use the Cable Calc App to check and verify 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.

This cable calculator also takes into account and applies the following factors for it's cable calculation formula:
- Voltage drop
- Correction factors
- Maximum disconnection time
- Length of circuit
- Installation method
- Cable type
- Tabulated Current
- Maximum Zs Values
- Calculate circuit Zs
- Calculate R1+R2
- Adjusted required minimum required cable ratings

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

How to use:
1) STEP 1 - Enter your cable calculation design parameters
2) STEP 2 - Select an installation method & apply any relevant correction factors
3) Tap "Calculate" to calculate the cable size
4) Print the cable calculation results

You may also like our 'Pro Certs' Electrical Certification App for iPad.

What’s New

Version 2.1.26

Cable Calc: Some optimisations and a dark mode bug fix.

Ratings and Reviews

2.5 out of 5
10 Ratings

10 Ratings

sparky#sparky ,


On step 2, there is a problem where you can not select the ambient temp without clicking on the two options below first. This needs fixing. (It says “no option”)
To improve this app, it would be helpful to allow you to select the wrong cable, and tell you which part doesn’t comply, and then you “+1 size” until the cable is compliant, where as you can not see the information now until you “go up a size”.
I.e. if the volt drop was none compliant etc, this would be useful but I guess may be difficult (and maybe not what it was designed for). I just thought I would feed this back.

Developer Response ,

Hi, the ambient temperature options depend on your selected installation method (ambient temp or ground temp), hence why you need to select an installation method first and why the Installation Method option is before the Ambient Temperature option.
- It the designers responsibility to select a suitable cable type for its intended use.
- When calculating a cable size if something does not comply you get a hint "Volt Drop Compliance Not Met: Try next size up" or "Max Zs Not Met: Try next size up?"

Mow2009 ,


It good but needs ring /radial circuits allowance!

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.

App Privacy

The developer, Pro Certs Software Ltd, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy.

Data Not Collected

The developer does not collect any data from this app.

Privacy practices may vary based on, for example, the features you use or your age. Learn More


  • Family Sharing

    Up to six family members can use this app with Family Sharing enabled.

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