Calculators
51 of them. Each one shows the formula it used and the standard it follows. Work through the explanation below any calculator and you can defend the number in a design review.
Cables & circuits
9 toolsSize the conductor, then prove the device protecting it fits.
- IS 732 · IS 3961
Cable Sizing Calculator
Size a copper or aluminium cable from load current, run length and installation conditions, with derating and volt drop both checked.
- BS 7671 18th Ed · Appendix 4
BS 7671 Cable Sizing Calculator — 18th Edition
Cable size, protective device and volt drop to BS 7671: reference method A to F, the Ca, Cg, Ci and BS 3036 correction factors, and Ib ≤ In ≤ Iz shown as a worked chain.
- AS/NZS 3008.1.1 · AS/NZS 3000
AS/NZS 3008 Cable Sizing Calculator
Cable size, device rating and volt drop to AS/NZS 3008 for Australia and New Zealand — five installation methods, V-75 against X-90, and the 40 °C air / 25 °C soil reference the standard actually uses.
- NEC / NFPA 70 · Table 310.16
NEC Wire Size Calculator — Ampacity, Breaker and Volt Drop
Size a conductor to the NEC with the rules most calculators skip: the 110.14(C) terminal temperature limit, the 240.4(D) small conductor rule, 125 % for continuous loads, and ambient and bundling correction.
- AWG · SWG (BS 3737) · IEC 60228
AWG to mm² Converter — Wire Gauge Chart
Convert between AWG, SWG and mm² in any direction, with diameter, resistance, the nearest stocked metric size and a warning when that nearest size has less copper than the gauge it replaces.
- IS 1554 · IS 7098 · IS 732
SWA Cable Sizing Chart
Current ratings for steel wire armoured cable across every size at once, derated for ambient, grouping and installation, with the longest run each size supports and a check on the armour as the circuit earth.
- IS 732 cl. 6.1
Voltage Drop Calculator
Check volt drop across a run in volts and percent against the 3 % lighting and 5 % power limits.
- IEC 60898 · IEC 60947-2 · Ib ≤ In ≤ Iz
MCB & MCCB Sizing Calculator
Pick the breaker rating, trip curve and breaking capacity for a circuit — and check it actually protects the cable rather than just fitting the load.
- IEC 60909
Short Circuit Current Calculator
Prospective fault current at any point, from transformer impedance and the cable run to it — with the minimum fault that decides whether the breaker trips.
Motors & drives
2 toolsFull load current, and the switchgear that goes around it.
- I = P / (√3 · V · pf · η)
Three-Phase Current Calculator
Full load current from kW, voltage, power factor and efficiency, for single and three-phase supplies.
- IS 732 · IEC 60947-4-1 AC-3
Motor Starter & Protection Sizing
Motor full load current, then the contactor, overload relay, breaker and cable that go around it — snapped to standard ratings.
Transformers & generation
4 toolsWhat feeds the board, and what it costs to run.
- IS 1180 · IEC 60076 · IEC 60909
Transformer Sizing & Fault Level
Full load current on both windings, how loaded the transformer really is, and the terminal fault current your switchgear has to break.
- Heat gain method · 1 TR = 12,000 BTU/hr
AC Tonnage Calculator
Air conditioner size from actual heat gain — area, roof, glass, occupants and equipment — plus running current, starting surge and yearly running cost.
- ISO 8528 · IS 13364
DG Set Sizing Calculator
Genset kVA from running load and from the largest motor start, whichever governs — plus altitude derating and fuel burn per hour.
- ISO 8528 · specific fuel consumption
DG Fuel Consumption Calculator
Litres per hour at any load point, cost per unit generated, and the load factor where a diesel stops being sensible.
Panels & earthing
5 toolsInside the enclosure: busbars, earth conductors, control supplies.
- NEC 625 · NEC 210.19 · NEC 220.83
EV Charger Load Calculator — Circuit & Panel Sizing
Breaker and wire size for an EV charger to NEC 625, and then the question that decides the job — whether the existing panel takes it, or whether the service has to be upgraded.
- Point-wiring practice · IS 732
Electrical Point Estimator
How many fans, light points, sockets and circuits a house or office needs, worked out from its rooms rather than from appliance wattages.
- IS 3043 · IEC 60364-5-54
Earthing Conductor Sizing
Size a protective earth conductor from fault current and clearing time by the adiabatic equation, cross-checked against the table method.
- IS/IEC 61439 · IEC 60909
Busbar Sizing Calculator
Pick a copper or aluminium bar for a panel from load current, ambient and enclosure — with the short-circuit force on the supports.
- Backplane and field supply budgeting
PLC I/O Power Budget Calculator
Backplane current against the CPU's supply, 24 V field load, and the power supply and heat budget for a control panel.
Energy cost & power quality
5 toolsWhat the units cost, and what distortion adds to the bill.
- S = P / cos φ
kW, kVA and kVAr Converter
Convert between real, apparent and reactive power, and find the capacitor rating needed to correct power factor.
- IEEE 1036 · IEC 60871 · IS 13340
Power Factor Correction Calculator — Capacitor Bank Sizing
kVAr to lift power factor to target, then the part that decides what you order — microfarads per element, star against delta, and what a capacitor rated for the wrong voltage actually delivers.
- Telescopic slab billing
Electricity Bill & Energy Cost Calculator
Units and rupees for any load, through a slabbed tariff rather than a flat rate — plus the payback on replacing it with something more efficient.
- ToD / TOU tariff structure
Time of Day Tariff Calculator
Peak, normal and off-peak energy costed separately, with what shifting load out of the peak band is worth.
- IEEE 519 · IEEE C57.110
Harmonic Distortion Loss Calculator
What current THD costs in extra copper loss, neutral current and transformer derating — with the money against it.
Metering & IoT
5 toolsGetting a number off a meter, and trusting it once you have it.
- IEC 61869-2 · class 0.5S
CT Ratio & Burden Calculator
Pick a current transformer ratio from the load, then budget the burden — which on a 5 A secondary is mostly cable, not meter.
- IEC 62053-22 · IEC 61869-2
Metering Accuracy & Billing Error
What a meter class is worth in units and money once the CT is included, at the load you actually run rather than at rated current.
- TIA/EIA-485-A · Modbus RTU timing
RS485 Cable Length & Poll Rate
Maximum bus length for a baud rate, how many devices a segment takes, and how fast you can actually poll them all.
- IEEE 754 · ABCD · CDAB · BADC · DCBA
Modbus Float Decoder
Paste two registers and see the value under all four byte orders at once. Settles word-order arguments in seconds instead of hours.
- Modbus data model vs PDU address
Modbus Address Converter
Convert between the 40001-style numbering manuals print and the protocol address that goes on the wire, with the right function code.
Solar & storage
5 toolsArray sizing and the battery bank behind it.
- P = ρgQH · Hazen-Williams · subsidy share
Solar Water Pump Sizing Calculator
Pump HP from real total head — water depth, delivery lift and pipe friction — plus the array to drive it without a battery, and the cost after the subsidy share.
- Rooftop subsidy · net metering · 25-year cash flow
Solar Payback & ROI Calculator
Rooftop cost after subsidy, the year it breaks even and the twenty-five year return — with tariff escalation, module degradation and export credit all carried through the cash flow.
- Diversity factor · VA vs W · start surge
Home Load Calculator
Build a house or office load appliance by appliance, then read the three figures that size an inverter: running VA after diversity, the worst starting surge, and the battery energy behind it.
- C10 rating · Peukert derating
Battery Bank & Backup Time
Ah, block count and real backup hours for an inverter or UPS bank, with the C10 discharge-rate penalty applied properly.
- kWp = E / (PSH · PR)
Solar Array Sizing Calculator
Array kWp, module count, inverter rating and roof area from daily consumption and local peak sun hours.
Electronics & components
5 toolsComponent markings and the small-signal end of the bench.
- V = I · R · P = V · I
Ohm's Law Calculator — Voltage, Current, Resistance & Power
Enter any two of V, I, R and P and get the other two, each shown with the expression that produced it — all twelve arrangements of the wheel in one solver, with worked examples and the series and parallel rules.
- R = (Vs − n·Vf) / If · IEC 60063
LED Resistor Calculator — Series Resistor & Power Rating
Series resistor for one LED or a chain: the E12 or E24 value you can actually buy, the current it really delivers, and the wattage to order.
- Vout = Vin · R2 / (R1 + R2)
Voltage Divider Calculator
Output from two resistors, solved either way round — and what a real load does to that output, which is where the textbook formula stops being true.
- EIA-198 · IEC 60062
Capacitor Code Calculator — Numeric, SMD & Colour Code Decoder
Decode 104, 223K or 4R7 into picofarads, nanofarads and microfarads at once — with the 8 and 9 multiplier exceptions and the EIA tolerance letters.
- IEC 60062
Resistor Colour Code Calculator
Read a resistor from its bands, or get the bands for a value you need. Three to six bands, with the tolerance range, temperature coefficient and nearest stocked E-series value.
Unit conversions
11 toolskW, kVA, VA, amps, volts and kWh — the same few equations, read whichever way round you need them.
- P(kW) = HP × 0.7457
HP to kW Calculator
Convert motor horsepower to kilowatts, in both mechanical and metric HP — and separate the shaft output from the electrical input the supply actually sees.
- HP = kW / 0.7457
kW to HP Calculator
Convert kilowatts to horsepower, mechanical and metric, with the caution that a kW input rating and a HP output rating are not the same quantity.
- I = HP × 746 / (√3 × V × PF × η)
HP to Amps Calculator
Full load current of a motor from its horsepower, with efficiency and power factor both applied — the two terms a straight HP to kW conversion leaves out.
- I = P × 1000 / (√3 × V × PF)
kW to Amps Calculator
Convert kilowatts to amps for single-phase and three-phase supplies, with power factor applied.
- P = √3 × V × I × PF / 1000
Amps to kW Calculator
Convert a measured current to kilowatts for single-phase and three-phase loads.
- I = S × 1000 / (√3 × V)
kVA to Amps Calculator
Convert transformer or generator kVA to full load current, single-phase or three-phase.
- I = P / (V × PF)
Watts to Amps Calculator
Convert watts to amps for DC, single-phase AC and three-phase AC circuits.
- P = S × PF
kVA to kW Calculator
Convert apparent power to real power. A 100 kVA set at 0.8 PF is an 80 kW set.
- S = P / PF
kW to kVA Calculator
Convert real power to apparent power. The gap between them is your power factor.
- VA = W / PF
Watts to VA Calculator
Convert watts to volt-amps — the conversion that decides what size UPS you buy.
- W = VA × PF
VA to Watts Calculator
Convert volt-amps to watts through the power factor.
Every calculator runs in your browser. Nothing you type is sent anywhere unless you choose to submit an enquiry. The blog works most of these through with real numbers.