Free Electronics Calculators
These tools cover the maths that comes up on a bench, in a van build or while planning a PCB. Enter your values and get resistor sizes, wire gauges, battery runtimes, antenna lengths and charging limits without a spreadsheet. Every calculator runs in your browser and nothing is uploaded.
Featured Electronics tools
- Ohm's Law & Power Triangle CalculatorEnter any two of voltage, current, resistance and power to get the other two.
- AWG Wire Gauge CalculatorGives the minimum wire size and voltage drop for a given current and run length.
- PCB Trace Width CalculatorSizes a trace for its current using IPC-2221, on external or internal layers.
- Battery Runtime CalculatorAdds up your devices and returns days of autonomy for a 12V battery bank.
Resistors & Circuit Basics
5 toolsSmall calculations that come up on almost every circuit: reading resistor bands, setting an LED current and dividing a voltage.
- Electronics / Students
Ohm's Law & Power Triangle Calculator
Enter any two of V, I, R, P and get all four values instantly with formulas shown. Smart unit prefixes, power rating, series/parallel resistor calculator.
- Electronics Hobbyists
Resistor Color Code
Click bands to decode resistance or type a value to get band colors. 4, 5, and 6-band support, E-series match, BOM builder.
- Electronics / Students
Voltage Divider Calculator
Enter any three of Vin, R1, R2, Vout and solve for the fourth. E24 nearest standard resistor values, current draw, power dissipation, loaded output.
- Electronics Hobbyists / Students
LED Resistor Calculator
Enter supply voltage, LED forward voltage, and desired current to get required resistance, nearest E24 value, power dissipation, and a simple circuit schematic.
- Electronics Hobbyists / Students
Capacitor Reactance & RC Circuit Calculator
Get capacitive reactance at any frequency, RC time constant, and -3dB cutoff frequency. pF, nF, µF, mF units.
Wire, Power & Batteries
4 toolsSize wire for a load, then estimate how long a battery or a power supply will keep it running.
- Electricians / Makers
AWG Wire Gauge Calculator
Enter current and run length to get minimum wire size, voltage drop %, and safety rating for DC 12V/24V and AC circuits.
- Electronics / Off-Grid
Battery Runtime Calculator
Free 12V battery runtime calculator for van builds, off-grid solar, and electronics. Add your devices, enter battery bank specs, and get days of autonomy and solar panel sizing.
- Oura / Ultrahuman Ring Owners
Smart Ring Battery Runtime Calculator
Estimate real-world Oura Ring or Ultrahuman Ring Air battery runtime based on the features you actually use.
- Local LLM / Home Server Hobbyists
Home AI Rig Electricity Cost Calculator
Estimate daily, monthly, and annual power cost of running GPUs for local LLM inference 24/7.
PCB Design
2 toolsTrace and via sizing for boards that carry real current.
- Electronics Engineers
PCB Trace Width Calculator
Calculate minimum PCB trace width per IPC-2221. External and internal layers, resistance, voltage drop, via current capacity, and multi-trace BOM table.
- PCB Designers & Electronics Makers
PCB Via Current Calculator
Enter drill diameter, copper plating thickness, and temperature rise to get max current (IPC-2221), via resistance, voltage drop, and parallel via capacity.
RF, Antennas & Audio
4 toolsAntenna lengths, link margins, impedance matching and speaker enclosure volumes.
- Amateur Radio
Ham Radio Antenna Calculator
Dipole, quarter-wave vertical, 5/8-wave vertical, and Yagi antennas. Enter frequency in MHz, get cut lengths in mm, cm, feet, and inches.
- Ham Radio / IoT / LoRa / FPV
Antenna Gain & Link Budget Calculator
Enter transmit power, antenna gains, frequency, and path distance to get path loss, received signal level, and link margin. Friis equation.
- Audio Engineers / Ham Radio
Impedance Matching & Transformer Ratio Calculator
Enter source and load impedances to get transformer turns ratio, mismatch loss, SWR, and power transfer.
- DIY Audio / Car Audio
Speaker Enclosure Volume Calculator
Enter Thiele-Small parameters to get optimal sealed and ported enclosure volumes, predicted -3dB point, and port dimensions.
Drones & RC
4 toolsMotor and propeller matching, flight time estimates, Remote ID rules and insurance cost ranges.
- RC / FPV Drone Builders
RC Motor KV & Prop Calculator
Enter motor KV, battery cell count, and prop size to get theoretical RPM, prop tip speed, and overspeed risk.
- FPV / Photography Drone Pilots
Drone Flight Time Calculator
Enter all-up weight, battery capacity, and voltage to estimate hover, cruise, and aggressive flight times with a 20% reserve. Battery comparison table.
- Drone Pilots / Hobbyists
Drone Remote ID Compliance Checker
Answer a few questions about your drone to find out if you need registration, Remote ID, or a broadcast module.
- Drone Pilots
Drone Insurance Cost Calculator
Estimate illustrative annual insurance cost ranges by drone weight class and use type - hobby or commercial.
USB-C, Docks & Home Networking
4 toolsFind where charging power or bandwidth is lost between a charger, a dock and your devices.
- Laptop / Phone Owners
USB-C PD Wattage Calculator
Find the actual wattage your charger and cable can deliver, and which one is the bottleneck if your device won't fast-charge.
- Laptop Dock / Hub Users
USB-C Dock Pass-Through Power Calculator
Find out how much wattage actually reaches your laptop through a dock once it takes its own share.
- Multi-Monitor / Daisy-Chain Setups
USB4 / Thunderbolt Bandwidth Calculator
See total bandwidth used by chained monitors and drives versus port capacity.
- Home Networking DIYers
Powerline Adapter Throughput Calculator
Enter your powerline adapter's advertised speed plus your wiring age and circuit distance to estimate realistic throughput.
Mobile Data Plans
3 toolsCompare what a data plan or an eSIM will cost for the way you use it.
- Mobile Hotspot / Satellite Internet Users
Data Cap Overage Cost Calculator
Project your data overage and overage fee before your billing cycle ends, based on your current usage pace.
- Heavy Mobile Data Users
Dual SIM Data Plan Stacking Calculator
Compare stacking two smaller eSIM data plans against one bigger single plan and see which is cheaper per GB.
- Travelers
eSIM Travel Data Cost Calculator
Line up Airalo, Holafly, Saily and other eSIM providers side by side for your actual trip length and data needs to see who's cheapest.
VR & AR Headsets
2 toolsFit and field-of-view numbers for headsets and smart glasses.
- VR / AR Headset Owners
VR IPD Calculator
Measure your interpupillary distance with a ruler and get the nearest valid setting for Quest 2, Quest 3, Quest Pro, Valve Index, PSVR2, Vive Pro 2, or Apple Vision Pro.
- AR / Smart Glasses Buyers
AR Glasses FOV Calculator
Compare two AR or smart glasses headsets on field of view and pixels per degree side by side. See which is wider and which is sharper.
Which tool do I need?
- Pick a resistor for an LEDLED Resistor Calculator
- Read the colour bands on a resistorResistor Color Code
- Set an output voltage with two resistorsVoltage Divider Calculator
- Solve for voltage, current, resistance or powerOhm's Law & Power Triangle Calculator
- Choose wire for a 12V or 24V runAWG Wire Gauge Calculator
- Estimate how long a battery bank will lastBattery Runtime Calculator
- Set the width of a PCB tracePCB Trace Width Calculator
- Cut a dipole or vertical antenna for a frequencyHam Radio Antenna Calculator
- Check whether a radio link has enough marginAntenna Gain & Link Budget Calculator
- Find out why a USB-C charger is slowUSB-C PD Wattage Calculator
- Estimate drone hover and cruise timeDrone Flight Time Calculator
- Check whether a drone needs Remote IDDrone Remote ID Compliance Checker
Electronics FAQ
How do I choose the right resistor for an LED?
Enter the supply voltage, the LED forward voltage and the current you want into the LED resistor calculator. It returns the required resistance, the nearest E24 value and the power the resistor dissipates.
What wire gauge do I need for a 12V circuit?
The AWG wire gauge calculator takes the current and the run length. It returns the minimum wire size, the voltage drop as a percentage and a safety rating, for DC 12V and 24V as well as AC circuits.
How wide should a PCB trace be?
Width depends on the current the trace carries and whether it sits on an outer or inner layer. The PCB trace width calculator applies IPC-2221 and also reports the trace resistance and voltage drop.
How long will a battery run my devices?
Add each device with its power draw and daily hours, then enter the battery bank specs in the battery runtime calculator. It returns days of autonomy and a matching solar panel size.
Why does my USB-C charger deliver less than its rating?
The wattage you get is limited by the weaker of the charger and the cable. The USB-C PD wattage calculator shows what the pair can deliver and which one is the bottleneck.
Do these calculators send my numbers anywhere?
No. Every calculation runs in your browser and nothing is uploaded.
Related categories
Last updated: September 30, 2026