Free Engineering Calculators You Can Trust
Size cables, motors, generators, pumps, batteries and solar systems in seconds. Every formula follows IEEE, IEC, NEC or BS 7671 and is checked by a senior electrical engineer.
- 500+ calculators
- Free, no sign-up
- Engineer reviewed
Most Used Calculators
- kW CalculatorReal power from V, A and PF
- kVA CalculatorApparent power, 1 and 3-phase
- kWh CalculatorEnergy use and running cost
- Amps to Cable SizeConductor size for a current
- Cable Voltage DropCheck drop over a cable run
- Motor FLAFull load amps from kW or HP
- Home Generator SizeRunning and starting watts
- Solar Panel CalculatorPanels for your daily use
- Battery Backup TimeRuntime of a battery bank
Calculators for Your Job
Start with the tools people in your trade use most.
Electrical Engineers
Solar Installers
HVAC & Pump Technicians
Advance Design Tools
Multi-step tools for complete system design, from load study to component list.
Generator Sizing Simulator
Size a generator from real load demand, diversity factor and site derating.
Open toolTransformer Sizing Calculator
Pick the transformer kVA rating for your connected load and future growth.
Open toolEarthing System Calculator
Grounding resistance, ground potential rise and touch and step voltage to IEEE 80.
Open toolPF Panel Component Calculator
Required kVAR, capacitor steps and a full bill of materials for a PFC panel.
Open toolIndustrial Solar Calculator
Plan a commercial or industrial solar system from site load and sunlight data.
Open toolCapacitor Color Code Decoder
Read capacitance, tolerance and voltage rating from standard color bands.
Open tool
Essential Electrical Formulas
A quick reference for the formulas behind our most used calculators. Click any card to calculate.
Single-Phase Power
P = V × I × PF
P in watts, V in volts, I in amps
Three-Phase Power
P = √3 × VL × I × PF
VL is the line-to-line voltage
Ohm's Law
V = I × R
R in ohms; also P = I² × R
Power Factor
PF = kW ÷ kVA
kVA² = kW² + kVAR²
Voltage Drop
Vd = 2 × L × I × R ÷ 1000
Single-phase; L in m, R in Ω/km
Energy
E = P × t
E in kWh, P in kW, t in hours
Built to Engineering Standards
Every calculator goes through the same four checks before it is published, so you can use the result on real projects with confidence.
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Sourced Formulas
Taken from the governing standard: IEEE, IEC, NEC, BS 7671, ASHRAE or NFPA.
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Tested on Real Cases
Checked against worked examples, edge cases and results from industry tools.
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Explained Results
Each tool shows the formula it uses and a step-by-step worked guide.
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Kept Up to Date
Calculators are revised when standards and best practice change.
Frequently Asked Questions
What is kW Calc?
kW Calc is a free library of 500+ engineering calculators covering power systems, cables, motors, generators, transformers, pumps, HVAC, batteries, solar and electric vehicles.
Are these calculators accurate?
Yes. They use industry-standard formulas from IEEE, IEC, NEC, BS 7671 and ASHRAE, and each one is reviewed by Nadeem Sial, a Senior Electrical Engineer with 15+ years of experience. For final designs, always check results against your local code.
Do I need an account?
No. Every calculator is free to use with no sign-up, subscription or login.
Does it work on my phone?
Yes. Every calculator works on phones, tablets and desktops.
What is the difference between kW and kVA?
kW is real power, the part that does useful work. kVA is apparent power, the total the supply has to deliver. They are linked by power factor: kW = kVA × PF. Generators and transformers are rated in kVA, while loads are usually rated in kW. Try the kVA to kW calculator.
Which standards do the calculators follow?
Each calculator uses the standard that governs that job, mainly IEC 60364, IEEE, the NEC (NFPA 70), BS 7671 for the UK, and ASHRAE for HVAC. The standard used is named on each calculator page.
Can I use the results for professional design work?
The calculators are built for engineers, electricians and installers and are a fast way to size and check a design. For work that must be certified or signed off, confirm the results against your local code and the equipment manufacturer's data.