Free electrical calculators
Small, honest calculators for students and technicians. Each page shows the formula, a worked example and the answer to common questions. They work in any browser, with or without JavaScript, and nothing you type is stored.
Transformer efficiency
Efficiency from iron and copper loss, and the load for maximum efficiency.
OpenMore electrical calculators
These calculators run in your browser and answer as you type.
Voltage Drop Calculator
Find how many volts a cable loses over its length, and the smallest cable size that keeps the drop inside your limit.
OpenStar-Delta (Y-Delta) Conversion Calculator
Convert between star and delta resistor networks, the standard step when simplifying bridge circuits and three-phase loads.
OpenMotor Full-Load Current and Breaker Size Calculator
Enter the motor rating, supply and power factor to get the full-load current, an indicative breaker size and the starting current for DOL and star-delta starters.
OpenBattery Backup Time and Inverter Size Calculator
Find backup time from battery size, or the battery size needed for the backup you want, with an indicative inverter rating.
OpenThree Phase Power Calculator (kW, kVA, kVAR)
Convert between voltage, current, kW, kVA and kVAR for single phase and three phase systems.
OpenInduction Motor Slip and Synchronous Speed Calculator
Calculate synchronous speed, slip and rotor current frequency, or find the rotor speed at a given slip.
OpenElectrical and Engineering Unit Converter
Convert the units that come up in electrical work: power, energy, torque, speed, length and cable cross-section.
OpenAWG to mm2 Wire Size Converter
Convert between American Wire Gauge and square millimetres, with conductor diameter and resistance.
OpenResistor Colour Code Calculator (4, 5 and 6 Band)
Choose the colour bands to get the resistance value, tolerance and range for 4, 5 and 6 band resistors.
OpenRC and RL Time Constant Calculator
Find the time constant, the time to reach a chosen percentage, and the cut-off frequency for RC and RL circuits.
OpenLED Series Resistor Calculator
Pick the resistor that sets the right current for one or more LEDs in series, with the next standard value and wattage.
Open555 Timer Calculator (Astable and Monostable)
Get the output frequency, duty cycle and timings for a 555 astable oscillator, or the pulse width of a monostable.
OpenSeries and Parallel Resistor, Capacitor Calculator
Combine any number of resistors, inductors or capacitors in series or parallel.
OpenStudent utilities
Useful for forms, exams and study. These run in your browser: your files and numbers are never uploaded.
Marks Percentage Calculator
Turn marks into a percentage and see how many marks you still need for a target.
OpenCGPA Calculator with Percentage Conversion
Add your semesters or subjects with grade points and credits to get a credit-weighted CGPA and an approximate percentage.
OpenPDF Tools: Merge, Extract Pages, Rotate and Images to PDF
Merge PDF files, pull out the pages you need, rotate pages or turn photos into a PDF. Your files stay on your device.
OpenImage Compressor and Resizer for Forms (KB and Pixels)
Set the width, height and largest file size you need, and download the compressed image. Nothing is uploaded.
OpenQR Code Generator (Text, Wi-Fi, UPI, WhatsApp)
Create a QR code for a link, Wi-Fi network, UPI payment or WhatsApp message, and download it as PNG or SVG.
OpenPomodoro Study Timer
Work in focused sessions with short breaks in between. Set your own lengths. The timer keeps accurate time in a background tab.
OpenElectrical Engineering Formula Flashcards
Revise machines, power and circuit formulas with flip cards. Add your own cards or import a deck.
OpenThe results are for learning and quick estimates. A real installation needs a proper design that follows the standards and the data sheets of the equipment you use.