Helpful tools for electricians
Proper calculators and lookups for the stuff you actually work out on jobs: voltage drop, cable sizes, max Zs, conversions, wiring colours, EICR codes, plus what you should really be charging. Built on the published BS 7671 tables, free forever, no catch.
Design & sizing calculators
Cable Size Calculator
Twin & earth and SWA sizing from the BS 7671 tables, with correction factors and a voltage drop check built in. Shows its working.
Open the calculatorVoltage Drop Calculator
Check any run against the 3% and 5% limits using proper mV/A/m values, plus the max length at your load.
Open the calculatorMaximum Zs Calculator
18th Edition max Zs for Type B, C and D devices, tabulated and 80% test values, with the full tables.
Open the calculatorAdiabatic Equation Calculator
Minimum CPC size from fault current, disconnection time and k factor. Reg 543.1.3 without the long division.
Open the calculatorEV Charger Cable Calculator
Size the circuit for a 3.6, 7.4, 11 or 22 kW charge point, continuous load, Section 722 flavoured.
Open the calculatorDownlight Spacing Calculator
How many downlights, what spacing, how far from the walls, from room size and ceiling height.
Open the calculatorConverters
Watts to Amps
W to A (and back) for 230 V mains, 12 V DC and three-phase, with a common-loads table.
Open the converterkW to Amps
Kilowatts to amps for single and three-phase, power factor included. Showers, hobs, EV chargers sorted.
Open the converterkVA to Amps
Generator and supply maths: kVA to amps at 230 V or 400 V three-phase, plus kVA vs kW explained.
Open the converterOhm's Law Calculator
Enter any two of volts, amps, ohms and watts, get the other two instantly with the formulas shown.
Open the calculatorLookups & decoders
Wiring Colours UK
Old vs new colour charts for single and three-phase, and whether red and black wiring needs replacing.
Open the chartIP Rating Checker
What IP65 actually means. Decode any rating and see where it's allowed, bathrooms and outdoors included.
Open the checkerBathroom Zones Checker
Zones 0, 1 and 2 with minimum IP ratings, what's allowed where, and the socket rules, interactively.
Open the checkerEICR Code Decoder
C1, C2, C3 and FI decoded: what each means, what it triggers, and which ones fail the report.
Open the decoderMoney tools
Day Rate Calculator
What you should actually charge per day, from the income you want, real overheads and honest billable days.
Open the calculatorCIS Tax Calculator
Subbie on CIS? Estimate your 2025/26 tax position and the refund you're probably owed.
Open the calculator The real toolA diary full of jobs
You found this page on Google. That's exactly how customers find electricians. I make sure that when they search in your area, it's you they find.
Message me on WhatsAppAll tools are guidance only. They use the published BS 7671 tables and current HMRC rates, but they don't know your installation or your books, so always verify against the standard, the On-Site Guide or your accountant. Spotted an error, or want a tool that doesn't exist yet? Email me and I'll build it.
Why are these free? Simple: you finding this page is the proof.
You googled something, and here you are, on an electrician SEO site. That's SEO working in the wild. Imagine the same trick pointed at "electrician near me" in your town, with your number at the top.
Tools save you minutes. Ranking #1 fills your diary.
I'm Jack, and I do SEO for electricians, nothing else. Leads don't grow in 90 days? I work for free till they do.* Fair?