Electronics Calculators and Tools for Laptop Repair
33 free calculators and helpers for board-level repair work: the maths behind dividers, regulators and sense resistors, SMD and colour code decoders, battery and charger numbers, and file tools for BIOS dumps. Everything runs in your browser — no sign-up, nothing uploaded.
Electrical basics
Ohm's law, dividers, resistor networks, LED resistors and RC timing.
- Ohm's Law CalculatorEnter any two of voltage, current, resistance or power and get the other two.
- Voltage Divider CalculatorOutput voltage of a two-resistor divider, or the resistor you need for a target voltage.
- Capacitor Discharge CalculatorStored energy, time to discharge to a safe voltage and peak current through a resistor.
- Capacitors in Series and Parallel CalculatorTotal capacitance of several capacitors in parallel or in series.
- LED Series Resistor CalculatorThe resistor an LED needs, the nearest standard value and the real current it gives.
- RC Time Constant CalculatorTime constant, settling time and cutoff frequency of any resistor and capacitor.
- Resistor Power and Package Rating CalculatorPower in a resistor and whether its SMD package size is rated for it.
- Resistors in Series and Parallel CalculatorTotal resistance of any number of resistors in series or in parallel, with each one's share.
Component codes and values
Decode SMD and colour codes, find standard values, package sizes and thermistor curves.
- SMD Resistor Code CalculatorDecode the number printed on a chip resistor: 103, 4R7, 1002, R010 or EIA-96 codes like 01C.
- Capacitor Code CalculatorTurn 104, 225K, 4n7 or 2A104J into pF, nF and µF with tolerance and voltage.
- NTC Thermistor Calculator (B Value)Temperature to resistance and back for NTC thermistors, plus the voltage the EC reads.
- Resistor Colour Code Calculator (4, 5 and 6 Band)Turn 4, 5 or 6 colour bands into a resistance value, tolerance range and tempco.
- SMD Package Size Converter (Imperial ↔ Metric)Imperial and metric chip sizes side by side — and why 0603 can mean two different parts.
- Standard Resistor Value Calculator (E6–E96)Nearest E6, E12, E24, E48 or E96 standard value to any number, with the error.
Power circuits
Regulator feedback, buck converters, LDO heat, sense resistors, PWM and chargers.
- Regulator Feedback Resistor CalculatorThe output voltage a feedback divider sets — or the resistor you need for a given rail.
- Buck Converter Calculator (Duty Cycle and Inductor Ripple)Duty cycle, inductor ripple and peak current of a step-down regulator.
- Current Sense Resistor CalculatorCurrent from the millivolts across a shunt, or the millivolts to expect at a given current.
- LDO Power Dissipation CalculatorHeat, efficiency and junction temperature of a linear regulator.
- Laptop Charger Compatibility and Wattage CalculatorCompare charger and laptop labels: voltage match, wattage and headroom.
- PWM Duty Cycle and Average Voltage CalculatorDuty cycle from the average voltage your meter shows, or the reverse, plus on- and off-time.
- USB-C Power Delivery CalculatorVoltage levels a USB-C PD charger offers, the cable's limit and whether it can charge a laptop.
Battery and charging
mAh and Wh, pack voltages, runtime and charging-time estimates.
- mAh to Wh Converter for Laptop BatteriesConvert battery capacity between mAh and watt-hours using the pack voltage.
- Battery Pack Voltage Calculator (Cells in Series and Parallel)Nominal, full and empty voltage and capacity of a pack from its S and P cell count.
- Laptop Battery Runtime CalculatorHow long a battery lasts at a given power draw, allowing for wear and reserve.
- Laptop Charging Time CalculatorHow long charging takes for a given battery, charger and load, with the slow final stage.
BIOS and firmware
SPI flash sizes, checksums, dump comparison, hex and MAC address helpers.
- SPI Flash Size Calculator (BIOS Chip Mbit to MB)Chip marking to size in MB and bytes — and whether a BIOS file fits the chip.
- File Checksum Calculator (SHA-256, SHA-1, CRC32)SHA-256, SHA-1 and CRC32 of a BIOS dump, computed locally, with blank-file and descriptor checks.
- BIOS Dump Compare ToolByte-by-byte comparison of two dumps with the differing address ranges listed.
- Hex, Decimal and Binary ConverterConvert addresses and register values between hex, decimal, binary and octal.
- MAC Address Converter and CheckerEvery format of a MAC address, the hex pattern to find it in a dump, and a validity check.
PCB and wiring
Jumper wire gauges, trace widths and board code identification.
- Laptop Board Code DecoderPaste a board code and see who made the board, the code family and matching catalog boards.
- Jumper Wire AWG CalculatorDiameter, resistance and voltage drop of thin copper jumper wire for a given length and current.
- PCB Trace Width Calculator (IPC-2221)Trace width for a current and temperature rise, plus its resistance and voltage drop.
How these calculators are meant to be used
Each tool answers one question that comes up at the repair bench: what voltage a feedback divider sets, how much a sense resistor drops, whether a replacement resistor will run too hot, how large a BIOS dump should be. Every page shows the formula, a worked example and the situations where the number matters on a laptop board.
The results are only as good as the values you enter. Take component values from the schematic or the part's datasheet, measure what you can, and treat the output as a check on your reasoning rather than a replacement for it. For background on the terms used, see the electronics glossary; for step-by-step repair procedures, see the guides.