Wattwise: Electrician Calc

Wattwise is the electrical calculator for electricians, engineers, installers and serious DIYers. 22 calculators and a full reference library, all offline, no account and no ads.

CABLES AND PROTECTION
• Cable size – smallest cable that meets both ampacity and voltage drop (IEC mm² or NEC AWG, copper or aluminium, correction factor)
• Voltage drop – drop in volts and percent, voltage at the load, cable losses
• Breaker size – standard breaker rating and matching minimum cable, NEC 125 % continuous-load rule
• AWG ⇄ mm² – diameter, area, circular mils and resistance
• Conduit fill (Pro) – fill percentage and maximum number of cables

BASICS
• Ohm's law – any two of voltage, current, resistance and power
• kW · kVA · amps – single-phase, three-phase and DC
• Power and energy unit converter – W, kW, hp, BTU/h, kcal, kWh, therm
• Energy cost – kWh and running cost per day, period and year

MOTORS AND POWER (Pro)
• Motor current – full-load current, DOL, star-delta and soft-start current, torque
• Power factor correction – capacitor kvar and µF, current before and after
• Transformer size – standard kVA rating and primary/secondary current
• Generator size – kVA for running loads plus motor starting surge

ENERGY, SOLAR AND BATTERIES
• Solar PV system (Pro) – panels, kWp, yearly production, battery bank, charge controller
• Battery runtime (Pro) – runtime, usable energy, C-rate, capacity for a target runtime

ELECTRONICS
• Resistor colour code with live 4/5-band preview
• LED resistor – nearest E12 value and wattage
• Series and parallel – resistors, capacitors, inductors

LIGHTING, HVAC AND PLUMBING
• Lighting design (Pro) – number of luminaires for a target lux level
• Air conditioner BTU – room cooling capacity
• Water heater time – heat-up time and energy
• Pipe flow (Pro) – water velocity and minimum pipe diameter

REFERENCE TABLES
Wire colour codes (IEC, USA, old UK), IP ratings, IEC and NEC ampacity tables, AWG table, standard breaker ratings and trip curves, E12/E24 resistor values, recommended lux levels and a full formula sheet.

MADE FOR THE JOB SITE
• Metric or imperial units, IEC or NEC tables, 50 or 60 Hz – set automatically for your country
• Every calculator shows the formula and explains how it works
• Share results as text
• 6 colour themes (orange, amber, sunset, copper, ocean, forest), light or dark
• English, Deutsch, Español, Français, Italiano, Português, Türkçe

WATTWISE PRO – ONE-TIME PURCHASE
Unlock 9 advanced calculators, save calculations per job and export professional PDF reports. No subscription. All future calculators included.

Results are estimates for planning. Always follow your local wiring code and have installations checked by a qualified electrician.