Ohm
Electronics and RF calculators
A resistor, a cutoff, a dipole, and the loss on the way to the antenna. Each page keeps the prefix and the citation next to the number.
Basics
Ohm's Law Calculator
Ohm’s law calculator for voltage, current, resistance, and power. Enter any two and read the other two.
Parallel Resistor Calculator
Parallel resistor calculator and series total. Up to five values, each with its own prefix.
Wavelength Calculator
Wavelength calculator for radio in vacuum or with a velocity factor, and for sound in air at a temperature you set.
Resistor Color Code Calculator
Resistor color code calculator for 4, 5, and 6 bands, in both directions, with an E12, E24, and E96 check.
Voltage Divider Calculator
Voltage divider calculator with a load, plus the nearest E12, E24, or E96 resistor pair for a target voltage.
Components
RC and LC Filter Calculator
RC filter calculator for low-pass, high-pass, and band-pass cutoff, with a Bode magnitude plot. Includes a resonant frequency calculator for an LC tank.
RC Time Constant Calculator
RC time constant calculator for tau, charge voltage, and discharge voltage, with the curve drawn out to five time constants.
LED Resistor Calculator
LED resistor calculator for one LED or a series string, the next E24 value up, and the resistor wattage at that current.
555 Timer Calculator
555 timer calculator for astable frequency and duty cycle, and for a monostable pulse, with the nearest standard resistor and capacitor.
RF & antennas
Dipole Antenna Calculator
Dipole calculator for half-wave and quarter-wave length, with ham band presets, velocity factor, and an end-effect factor.
Impedance and Reactance Calculator
Impedance calculator for inductive and capacitive reactance, and for series or parallel RLC magnitude and phase.
Free-Space Path Loss Calculator
Free space path loss calculator with EIRP, received power, fade margin, and the first Fresnel zone radius at mid-path.
Coax Loss Calculator
Coax loss calculator for LMR-240, LMR-400, LMR-600, RG-58, RG-8X, and RG-213 from the manufacturer attenuation table or formula.
SWR Calculator
SWR calculator from the reflection coefficient, a real load impedance, return loss, or forward and reflected power, with mismatch loss.
PCB
How these calculators work
The basic tools are Ohm’s law, series and parallel resistors, the color code in both directions, a wavelength for radio or for sound, and a voltage divider that can pick an E12, E24, or E96 pair. Resistance, capacitance, and inductance take a prefix, p through G, so a picofarad is not typed as 0.000000000001. The color-code page names every band in text. The swatch is only a picture of that name.
Component tools cover an RC low-pass or high-pass, a series RLC band-pass, and the LC resonant frequency on the same page, plus the RC charge curve, an LED resistor with the next standard value up, and a 555 in astable or monostable. The astable period uses ln(2). The monostable pulse uses 1.1, the constant printed on the TI LM555 data sheet. None of these pages is a substitute for the part’s absolute-maximum ratings.
RF tools give a half-wave and a quarter-wave with a velocity factor and an end-effect factor, reactance and series or parallel impedance, free-space path loss with a first Fresnel radius, coax attenuation from Times Microwave formulas or Belden tables, and SWR from the reflection coefficient. The microstrip page uses the IPC-2141 wide and narrow forms of the Hammerstad equations, with zero copper thickness and no solder mask. A fabricator’s stackup replaces that estimate. Ham presets are band centers for planning a length, not an antenna design.