Free tools
Free tools for UK electricians
Calculators and cost estimators for the everyday jobs: cable sizing, max Zs, diversity, EICR coding and more. No sign-up, no paywall. Built by the team behind SparkCerts, the job, certificate and invoice app for UK electricians.
Cable size calculator
Minimum cable size from design current, method and length, with a volt drop check.
Max Zs checker
Maximum earth fault loop impedance for any MCB or RCBO.
R1+R2 & expected Zs
Expected R1+R2 and Zs from conductor sizes and length, with the longest run before Zs fails.
RCD trip-time limits
Maximum BS 7671 disconnection times at 0.5, 1 and 5 times the rated current.
Maximum demand and diversity
Estimate a home's maximum demand using BS 7671 diversity.
EICR code checker
The code a common observation usually attracts: C1, C2, C3 or FI.
Prospective fault current
Work out PFC from voltage and loop impedance, and check breaking capacity.
kW to amps converter
Convert between power and current for single and three phase loads.
Sockets on a ring main
How many sockets and spurs a ring final or radial circuit can serve.
Adiabatic / CPC size
Minimum protective conductor size from fault current and disconnection time.
Earthing & bonding size
Main earthing and main protective bonding conductor sizes for the supply.
Lighting / lux calculator
How many fittings a room needs for a target lux level.
Voltage drop calculator
Volt drop for a run, checked against the 3% and 5% limits.
EV charger install cost
Estimate the cost of fitting a home EV charge point in the UK.
Fuse board replacement cost
Estimate the cost of a new consumer unit in the UK.
House rewire cost
Estimate the cost of rewiring a UK home by size, scope and region.
EICR cost estimator
Estimate the cost of an Electrical Installation Condition Report.
What an electrician costs
Typical UK call out, hourly and day rates by region.
Built on the BS 7671 tables you certify with
Every tool here uses BS 7671 and the IET On-Site Guide. The design calculators (cable size, max Zs, diversity, fault current) use the same tables you put on a certificate, so the figure you get on your phone is the figure that belongs on the schedule. The cost estimators use realistic UK supplied and fitted prices, so you can give a customer a sensible number on the spot.
They are free and need no account. Each one also shows what SparkCerts does once the job is real. The app carries these readings onto BS 7671 model-form certificates, flags an impossible result while you are still on site, and turns the work into a quote and an invoice.