Power · Generators · Cables · Transformers · Storage
Electrical calculations you can check line by line.
Nine calculators for power engineers and students. Every result shows the formula with your own numbers substituted, the assumptions behind it, and the limits of what it can tell you.
Calculators by topic
Power & current
Line current, kW, kVA and kVAr for single- and three-phase circuits.
- Line currentCalculate line current from kW, hp or kVA for three-phase (line-to-line or line-to-neutral) and single-phase supplies, with PF, efficiency and every step shown.
- kVA ↔ kW ↔ kVArConvert between kVA, kW and kVAr using power factor, solve the power triangle from any two values and get the matching line current.
Generators
Diesel genset sizing with motor starting, and fuel use at part load.
- Generator sizingSize a generator set from a load table: running kW/kVA, diversity, motor starting kVA by DOL, soft starter or VFD, margin, derating and a common kVA rating.
- Generator fuel useEstimate diesel generator fuel use in L/h from load and specific fuel consumption with an editable part-load curve, plus daily use, tank runtime and cost.
Cables
Voltage drop with temperature-corrected resistance and a size solver.
Transformers & PF
Transformer loading and losses, capacitor banks for power factor.
- Transformer loadingFind transformer percentage loading, full-load currents on both windings, copper loss scaled with load squared, total losses and efficiency at the actual load.
- PF correctionCalculate capacitor kVAr to raise power factor, capacitance per phase for star and delta banks at 50 or 60 Hz, and the resulting line current reduction.
Batteries & solar
Battery runtime with Peukert, and off-grid PV array and bank sizing.
- Battery runtimeEstimate battery bank runtime from Ah, voltage, depth of discharge and inverter efficiency, with an optional Peukert correction and a series/parallel bank builder.
- Solar PV sizingSize an off-grid solar PV system: array kWp and panel count from daily energy and peak sun hours, battery Ah for days of autonomy, and charge controller current.
What every calculator gives you
The working, not just a number
Each step is written out with your inputs substituted, so you can follow the arithmetic or copy it into a calculation sheet.
Assumptions stated
Balanced load, conductor temperature, part-load fuel curve, Peukert exponent: whatever the result depends on is listed next to it and can be changed.
Tested logic
The calculation code is separate from the page and checked by automated tests against hand-worked examples. The methodology page lists them.
Results are estimates for learning and preliminary design. Final designs must follow the applicable code (IEC 60364, NEC/NFPA 70, BS 7671 or local rules), the manufacturer's data and the judgement of a qualified engineer. Everything runs in your browser and nothing you type is uploaded.
Guides
- kW vs kVA: Power Factor in Plain TermsWhy generators and transformers are rated in kVA while loads are rated in kW, what power factor really measures, and how to convert between them without mistakes.
- How to Size a Diesel Generator for Motor LoadsA practical method for sizing a diesel generator when motors are involved: running load, starting kVA, starting method, voltage dip and site derating.
- Voltage Drop: Why Long Cable Runs Need Bigger ConductorsHow resistance, reactance, temperature and length combine to cause voltage drop, why limits like 3 % and 5 % exist, and when to upsize a cable.