Watts to dBm Conversion Calculator

Watts to dBm Calculator

Enter power in watts:

dBm result: dBm

A Watts to dBm calculator converts absolute power measurements between watts (W) and decibel-milliwatts (dBm), the logarithmic unit used in:

✅ RF & microwave engineering
✅ Telecommunications
✅ Fiber optic systems
✅ Signal strength analysis

Key Definitions

• Watt (W): SI unit of absolute power

• dBm: Decibels relative to 1 milliwatt (0 dBm = 1 mW)

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Conversion Formulas

1. Watts to dBm

$$P(dBm)=10\times {\log }_{10}\left(\frac{P(W)}{0.001}\right)$$

Simplified:

$$P(dBm)=10\times {\log }_{10}(P(W))+30$$

Example:
Convert 2 W to dBm:

$$10\times {\log }_{10}(2)+30\approx 33.01\text{ dBm}$$

2. dBm to Watts

$$P(W)=0.001\times {10}^{(P(dBm)\mathrm{/}10)}$$

Example:
Convert 20 dBm to W:

$$0.001\times {10}^{(20\mathrm{/}10)}=0.1\text{ W}$$

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Conversion Table (W ⇆ dBm)

Watts (W)	dBm	Typical Application
0.000001 W	-30 dBm	Minimum detectable signals
0.001 W	0 dBm	Reference level (1 mW)
0.01 W	10 dBm	WiFi routers
0.1 W	20 dBm	Small RF transmitters
1 W	30 dBm	Mobile base stations
10 W	40 dBm	Commercial transmitters
100 W	50 dBm	Broadcast equipment

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How to Use the Calculator

1. Enter Watts → Get dBm

   • Multiply W by 1000 to get mW

   • Take 10 × log₁₀(mW value)

2. Enter dBm → Get Watts

   • Calculate 10^(dBm/10)

   • Multiply by 0.001

Example Calculations:

• 5 W to dBm:

  $$10\times {\log }_{10}(5000)\approx 36.99\text{ dBm}$$

• -10 dBm to W:

  $$0.001\times {10}^{(-10\mathrm{/}10)}=0.0001\text{ W}$$

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Practical Applications

• Cellular Networks: Phone TX power ~23 dBm (0.2 W)

• Fiber Optics: Laser power 0 dBm (1 mW) to 10 dBm (10 mW)

• WiFi: Max legal power ~30 dBm (1 W)

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Key Reference Points

Power Level	dBm	Watts
Maximum WiFi	30 dBm	1 W
Standard WiFi	20 dBm	0.1 W
Bluetooth	0 dBm	0.001 W
Minimum signal	-80 dBm	0.00000001 W

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FAQ

1. Why use dBm instead of watts?

🔹 Logarithmic scale handles huge power ranges
🔹 Simplifies calculations (multiplication becomes addition)
🔹 Standard in RF engineering

2. Is 0 dBm equal to 0 watts?

❌ No! 0 dBm = 1 mW = 0.001 W

3. How many watts is 40 dBm?

✅ 40 dBm = 10 W
(10^(40/10) × 0.001)

4. What does negative dBm mean?

🔹 Power levels below 1 mW
🔹 -30 dBm = 0.000001 W

5. How to convert 25 W to dBm?

$$10\times {\log }_{10}(25000)\approx 43.98\text{ dBm}$$