Ohmlark

Nine free calculators for people who build circuits: resistor color code, LED resistor, voltage divider, RC filter, LC resonance, 555 timer, battery life, IPC-2221 PCB trace width and an electronics unit converter. Results use E12/E24/E96 standard values and show the power rating you need. No account needed. Pro ($4/month or $29 lifetime) adds saved projects, a BOM cost and battery-runtime sheet, and PDF/CSV export.