BS 7971 cable size calculator, calculate cables sizes, volt drop, r1+r2 and max zs 18th edition cable calculator.

An easy to use cable calculator to calculate the required cable sizes for various cables types, installation methods, correction factors and protective devices to BS 7671 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)

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 cable calculation results

A handy cable size calculator 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 and Electrical Certification Software for iOS:

What’s New

Version 1.3.7

Added 90°C singles, new optional Circuit Ref input, new optional Circuit Description input.

Ratings and Reviews

2.9 out of 5
8 Ratings

8 Ratings

Mow2009 ,


It good but needs ring /radial circuits allowance!

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?"

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 will be able to use this app with Family Sharing enabled.

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