About this tool
In radio engineering power is usually given in dBm, i.e. decibels relative to 1 mW: 0 dBm is 1 mW, 20 dBm is 100 mW, 30 dBm is 1 W. The dBm converter turns a value in dBm, dBW, W, mW or µW into all other units.
Receivers and test equipment often state levels as a voltage in µV or dBµV. At an impedance of 50 Ω, 0 dBm equals 223.6 mV or 106.99 dBµV; switch to 75 Ω (TV, satellite, cable networks) or a custom value in the advanced parameters.
The converter also computes EIRP and ERP from transmit power, antenna gain and cable loss, as well as field strength and power density in the far field. For a complete radio link with received power and range, use the Link Budget Calculator. All calculations run in your browser.
How it works
- Enter a value and choose its unit – dBm, dBW, W, mW, µW, dBµV, dBmV, V, mV or µV.
- Read all other units from the table, or click a common value in the list.
- Turn on the advanced parameters for another impedance, EIRP/ERP with antenna gain and cable loss, and the field strength at a distance.
Frequently asked questions
How do I convert dBm to watts?
P in W = 10^((dBm − 30) / 10). The other way round, dBm = 10·log10(P / 1 mW). Every 10 dB is a factor of 10 and every 3 dB roughly a factor of 2: 20 dBm is 100 mW, 23 dBm about 200 mW, 30 dBm 1 W and 37 dBm about 5 W.
How are dBm and dBµV related?
Through the impedance: P = V²/R. At 50 Ω, dBµV = dBm + 106.99, at 75 Ω dBµV = dBm + 108.75. A received level of −100 dBm at 50 Ω is therefore 6.99 dBµV or 2.24 µV. An S9 signal on shortwave (50 µV at 50 Ω) is −73 dBm.
What is the difference between EIRP and ERP?
EIRP (equivalent isotropically radiated power) refers the antenna gain to an imaginary isotropic radiator (dBi), ERP to a half-wave dipole (dBd). Since the dipole has a gain of 2.15 dBi, the ERP is always 2.15 dB lower than the EIRP. Limits for radio applications are given in EIRP or ERP depending on the frequency band.
How is the field strength calculated?
In the far field of a radiator in free space, E = √(30·P)/d with P as EIRP in W and d in m, and the power density is S = P/(4π·d²). 1 W EIRP therefore produces about 0.55 V/m at 10 m. The formula ignores ground reflections, the near field and side lobes of the antenna – human exposure needs a proper assessment.