Interactive Electromagnetics Calculators

Use calculators as a check, not a substitute for assumptions.Every result below states the idealized relation being used. Real systems can differ because of loss, mismatch, finite geometry, calibration, dispersion, loading, temperature, and measurement uncertainty.

Frequency ↔ wavelength

$\lambda=c/f$ in free space.

Free-space path loss

$FSPL=20\log_{10}(4\pi R/\lambda)$.

Frequency (GHz)

Distance (m)

Friis received power

$P_r=P_tG_tG_r(\lambda/4\pi R)^2$.

$P_t$ (dBm)

$G_t$ (dBi)

$G_r$ (dBi)

Frequency (GHz)

Distance (m)

Thermal noise floor

$P_n\approx-174+10\log_{10}B+NF$ dBm near 290 K.

Bandwidth (Hz)

Noise figure (dB)

Skin depth

$\delta=1/\sqrt{\pi f\mu\sigma}$.

Frequency (MHz)

Conductivity (S/m)

Relative permeability

Rectangular waveguide TE$_{10}$ cutoff

$f_c=c/(2a\sqrt{\epsilon_r})$.

Broad wall $a$ (mm)

$\epsilon_r$

Radar range resolution

$\Delta R\approx c/(2B)$.

Bandwidth (MHz)

Monostatic Doppler shift

$f_D=2v_r/\lambda$.

Frequency (GHz)

Radial velocity (m/s)

Larmor frequency

$f_L=(\gamma/2\pi)B$. Enter $\gamma/2\pi$ in Hz/T.

$\gamma/2\pi$ (Hz/T)

Field (µT)

Electric-dipole Rabi frequency

$\Omega=dE/\hbar$ for a fully projected dipole moment.

Dipole (ea$_0$)

Electric field (V/m)

Ideal Halbach-cylinder bore field

$B\approx B_r\ln(R_o/R_i)$ for an ideal infinitely long $p=1$ cylinder.

$B_r$ (T)

$R_i$ (mm)

$R_o$ (mm)

Assumptions to remember

Free-space link equations assume far-field propagation and do not include cable loss, polarization mismatch, multipath, atmospheric loss, or mismatch unless added separately.
Skin depth assumes a good conductor and sinusoidal steady state.
The waveguide expression is for the dominant TE$_{10}$ mode in an ideal rectangular guide.
Radar resolution uses waveform bandwidth, not carrier frequency.
Larmor and Rabi calculators require the correct state-dependent gyromagnetic ratio or projected transition matrix element.
The Halbach expression is an ideal limit; segmentation, finite length, temperature, tolerances, and nearby magnetic material change the result.

See Worked Examples, Scaling Laws, and Measurements & Instruments for context.