dBm⇔ワット 変換ツール
RF電力の双方向換算
Required Parameters
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Quick Answer
dBm is an absolute power measurement referenced to 1 milliwatt (mW). 0 dBm = 1 mW. Every 3 dB increase doubles the power; a 10 dB increase multiplies power by 10.
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澶夋彌鍏紡
P(mW) = 10^(dBm/10)
dBm = 10 x log10(P/1mW)
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Design Notes
Using dBm makes calculating signal chains incredibly simple by substituting multiplication/division with addition/subtraction. For example, if you output +10 dBm, pass it through a -3 dB attenuator, and add a +15 dB amplifier, the output is simply 10 - 3 + 15 = +22 dBm. Note that in 50Ω systems, 0 dBm corresponds to ~223.6 mV(RMS).
Common Mistakes
- 1
Confusing dBm (absolute power) with dB (relative ratio). You can add dB to dBm, but adding dBm to dBm is mathematically invalid.
- 2
Forgetting that negative dBm still represents positive Watts (e.g., -30 dBm is 1 microwatt, not 'negative power').
- 3
Assuming the calculation depends on impedance. Power to dBm conversion is pure power mapping independent of impedance, though converting it safely to Voltage requires knowing Z0.
Engineering Handbox
1. Use formula: P(W) = 10^(dBm / 10) / 1000 2. 10^(30/10) = 10³ = 1000 3. 1000 / 1000 = 1 Watt
Knowledge Base
dBmとは？
1mW基準のデシベル表現。0 dBm = 1 mW。3dBごとに電力2倍、10dBで10倍。
dBmからワットへの変換は？
P(W) = 10^(dBm/10) / 1000。例：30 dBm = 10³ mW = 1W。
dBmとdBの違いは？
dBmは絶対値（1mW基準）。dBは相対比。dB + dBm = dBm。dBm + dBm は不可。
覚えておくべきdBm値は？
0=1mW、+10=10mW、+20=100mW、+30=1W。負側：-10=0.1mW、-30=1µW、-60=1nW。
WiFiの信号強度の目安は？
優良：-30〜-50dBm、良好：-50〜-67dBm、弱い：-72〜-80dBm、使用不可：-80dBm以下。