Question 1

What is dBm?

Accepted Answer

dBm (decibels relative to milliwatt) is a logarithmic power unit referenced to 1 mW. Formula: dBm = 10 × log₁₀(P_watts / 0.001). Common in RF/wireless: 0 dBm = 1 mW, 30 dBm = 1 W, -30 dBm = 1 µW. Logarithmic scale makes large power ranges easy to work with.

Question 2

How do I convert dBm to watts?

Accepted Answer

Rearrange the formula: P (watts) = 10^(dBm/10) / 1000. Example: 20 dBm = 10^(20/10) / 1000 = 100 / 1000 = 0.1 W = 100 mW. Use a calculator or this tool to avoid errors.

Question 3

How do I convert watts to dBm?

Accepted Answer

Formula: dBm = 10 × log₁₀(P_watts × 1000). Example: 0.1 W = 100 mW = 10 × log₁₀(100) = 10 × 2 = 20 dBm. Reverse of dBm-to-watts conversion.

Question 4

What is dBW?

Accepted Answer

dBW (decibels relative to watt) is referenced to 1 W instead of 1 mW. Formula: dBW = 10 × log₁₀(P_watts). Relationship: dBm = dBW + 30 (since 1 W = 1000 mW). Used in high-power RF applications.

Question 5

Why use logarithmic scales in RF?

Accepted Answer

RF power spans huge ranges: transmitters (watts), receivers (-100 dBm ≈ picoatts). Logarithmic scales compress this range into manageable numbers. Also, signal path gains/losses add linearly in dB, simplifying calculations.

Question 6

What is a typical transmitter power in dBm?

Accepted Answer

WiFi: 20–30 dBm (~100 mW–1 W). Cellular: 20–43 dBm (100 mW–20 W). Amateur radio: 5–50 dBm (micropower to 100 W). Satellite: 30–50 dBm. Check local regulations; transmit power is often limited.

Question 7

What is receiver sensitivity?

Accepted Answer

Receiver sensitivity is the minimum power a receiver can detect. Typical values: -100 to -120 dBm (WiFi), -150 dBm (satellite). Expressed in dBm because signals are so weak. Lower (more negative) = better sensitivity.

Question 8

What is link budget?

Accepted Answer

Link budget: Tx power (dBm) + Tx antenna gain - path loss + Rx antenna gain - losses = Rx power (dBm). If Rx power > Rx sensitivity, link works. All calculations in dBm make budgeting straightforward.

Question 9

How do I add/subtract power in dB?

Accepted Answer

Adding power (linear): P_total (W) = P1 + P2, then convert to dBm. In dB directly: 10 dBm + 10 dBm ≠ 20 dBm (anti-intuitive). Always convert to linear watts for addition/subtraction, then convert back to dB if needed.

Question 10

What is a milliwatt vs. a watt in RF?

Accepted Answer

1 W = 1000 mW = 0 dBW = 30 dBm. Milliwatts are common in handsets, WiFi, and low-power RF. Watts are used in base stations, broadcast, and high-power amplifiers.

Question 11

Is 20 dBm a lot of power?

Accepted Answer

20 dBm = 100 mW. Moderate power—typical for WiFi, Bluetooth LE, and cellular handsets. For RF, "a lot" is relative: 30 dBm (1 W) is moderate; 43 dBm (20 W) is high for mobile; 50+ dBm is very high-power RF.

Question 12

What is ERP and EIRP?

Accepted Answer

ERP (Effective Radiated Power) = transmitter power + antenna gain relative to dipole. EIRP (Effective Isotropic Radiated Power) = same but referenced to isotropic antenna. Both in dBm or dBW. Used to calculate link budget and regulatory compliance.

dBm to Watts Converter

Key Formulas & References

RF Power Scale & Applications

dBm	Watts	Application
-120 dBm	1 pW	Satellite receiver, deep space
-100 dBm	0.1 nW	WiFi sensitivity limit
-60 dBm	1 nW	Weak signal (far from AP)
-30 dBm	1 µW	Low-power sensor
0 dBm	1 mW	Bluetooth LE, NFC
10 dBm	10 mW	Bluetooth Classic
20 dBm	100 mW	WiFi, cellular handset
30 dBm	1 W	Mobile phone max (typical)
43 dBm	20 W	Cellular base station (per channel)
50 dBm	100 W	FM broadcast transmitter