RF Calculators

Common radio frequency calculations.

Calculator	Description
Enter either: Frequency MHz Wavelength m Result: —	Converts between frequency and free-space wavelength. Fundamental for antenna design, band planning, and understanding propagation. λ = c / f — λ(m) = 299.792 / f(MHz)
Enter any two: V I R Result: —	Ohm's Law. The foundation of all circuit analysis; enter any two values to find the third. Used everywhere from power supply design to transmission line calculations. V = I × R
Enter: V I Result: —	Electrical power from voltage and current. Essential for sizing power supplies, calculating heat dissipation, and staying within transmitter ratings. P = V × I
Enter: Frequency MHz Result: —	Total length of a half-wave dipole antenna. The 468 constant accounts for the end effect that makes a real-world dipole slightly shorter than a free-space half wavelength. L(ft) = 468 / f(MHz)
Enter: Frequency MHz Result: —	Length of a quarter-wave vertical antenna or ground-plane radial. Used for vertical antennas, mobile whips, and ground-plane designs. L(ft) = 234 / f(MHz)
Enter either: dBm Watts Result: —	Converts between dBm and watts. dBm is the standard unit for RF power levels in test equipment, receiver sensitivity specifications, and link budgets. P(W) = 10^{(dBm − 30) / 10}
Enter: Forward W Reflected W Result: —	VSWR and return loss from forward and reflected power, as read on an SWR meter or directional coupler. Key metric for antenna tuning and feedline health. Γ = √(P_r / P_f), VSWR = (1 + Γ) / (1 − Γ)
Enter: L µH C pF Result: —	Resonant frequency of a series or parallel LC circuit. Used to design filters, matching networks, crystal oscillators, and tuned amplifier stages. f = 1 / (2π√LC)
Enter: Distance km Frequency MHz Result: —	Free-space path loss for line-of-sight links. The baseline loss before accounting for antenna gains, cable losses, and atmospheric effects. Essential for VHF/UHF/microwave link budgets. FSPL(dB) = 20 log₁₀(d) + 20 log₁₀(f) + 32.44
Enter: Antenna height m Remote height m Result: —	Maximum line-of-sight distance between two antennas over a smooth Earth, accounting for standard atmospheric refraction (k = 4/3). Enter both antenna heights; if only one is given the remote height defaults to zero (ground level). d(km) = 4.12 × (√h₁ + √h₂)
Enter: TX power W Ant. gain dBd Line loss dB Result: —	Effective Radiated Power. Combines transmitter power, antenna gain, and feedline loss. Used to verify compliance with band-specific power limits and for link budget planning. ERP(dB) = P_dBm + G_dBd − L_dB
Enter: Physical length m Velocity factor Result: —	Electrical length of a coaxial cable segment. Signals travel slower than light in coax; the velocity factor (typically 0.66 for solid PE, 0.82 for foam) shortens the effective wavelength. Critical for phasing harnesses and stub filters. L_elec = L_phys ÷ VF
Enter: Frequency MHz Resistivity µΩ·cm Result: —	Skin depth — the depth at which current density drops to 1/e. At RF, current flows only in a thin surface layer. Determines minimum conductor plating thickness (e.g. silver-plated wire). Default resistivity is copper. δ = √(ρ / πfμ₀)