RF & Electronics Reference Library
Practical formulas, solved examples, and free interactive calculators for RF technicians, electronics students and engineers. Check application conditions and component ratings before using calculated results in hardware.
dBm to milliwatts
Power in decibels relative to one milliwatt. Formula:
P(mW) = 10dBm/10
0 dBm = 1 mW; 30 dBm = 1 W.
Open dBm calculator →Watts to dBm
Express power on a logarithmic scale.
dBm = 10 × log10(P(W) × 1000)
0.1 W = 20 dBm; 1 W = 30 dBm.
Open watts to dBm →VSWR and return loss
Relate standing-wave ratio to the reflection coefficient.
|Γ| = (VSWR − 1) / (VSWR + 1)
Return loss = −20 log10(|Γ|). At 2:1 VSWR, return loss is about 9.54 dB.
Open VSWR calculator →Wavelength
Use the speed of light to estimate free-space wavelength.
λ = c / f; c = 299,792,458 m/s
100 MHz is approximately 3 m free-space wavelength. In cable, use its velocity factor.
Open wavelength calculator →Ohm’s law and resistor power
Calculate ideal resistive circuit current and dissipation.
I = V/R; P = V²/R
12 V across 100 Ω yields 0.12 A and 1.44 W. Check resistor power ratings.
Open Ohm’s law calculator →Further electrical tools
Resistor power · Parallel resistors · Voltage divider · Capacitor energy
All tools are free, with no sign-in required.