Signal Strength
Calculate received wireless signal strength from transmit power, distance and path loss.
About Signal Strength
dBm is a logarithmic power unit referenced to 1 milliwatt: dBm = 10·log10(power_in_mW). This logarithmic scale compresses the enormous dynamic range of wireless signal power (from nanowatts to watts) into a compact, easy-to-work-with number, and — since it's logarithmic — gains and losses along a signal path can simply be added or subtracted in dB rather than multiplied or divided, which is why link budgets are always computed in dBm/dB.
Formulas
dBm to milliwatts
mW = 10^(dBm / 10)
Milliwatts to dBm
dBm = 10 × log10(mW)
Worked example
With the default values below, Signal Strength returns dBm of -65.000. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Input Unitone of dBm, Milliwatts (mW), Microwatts (µW)
- dBm
- Value
- -65
Results
- dBm
- -65.000 dBm
- Milliwatts
- 0.000000 mW
- Microwatts
- 0.000 µW
Step by step
- 1Values used
- 2dBm to milliwatts
- 3Milliwatts to dBm
- 4dBm= -65.000 dBm
- 5Milliwatts= 0.000000 mW
- 6Microwatts= 0.000 µW
Assumptions and limits
- The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 6 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why use dBm instead of watts or milliwatts directly?
Wireless signal power spans many orders of magnitude, from picowatts of noise to watts of transmit power. The logarithmic dBm scale compresses this into small, manageable numbers, and critically, lets path losses and gains be added/subtracted rather than multiplied/divided.
What does 0 dBm equal?
0 dBm equals exactly 1 milliwatt (1 mW), since dBm is defined relative to that 1 mW reference.
Why is WiFi signal strength always shown as a negative dBm value?
Because received wireless signals are almost always weaker than 1 mW after traveling through air and obstructions, so their dBm value is negative — e.g. -50 dBm (strong) is about 10 microwatts, while -90 dBm (weak) is about 1 nanowatt.
How do I add two dBm power levels together?
You can't add dBm values directly — convert each to mW (or W) first, add the linear values, then convert the sum back to dBm. Only gains/losses expressed in dB (not absolute power in dBm) can be added or subtracted directly.