dBm to Watts Excel Formula Guide
Copy-paste verified formulas to convert decibel-milliwatts (dBm) to Watts, milliwatts (mW), and RMS voltage across Microsoft Excel, Google Sheets, and LibreOffice Calc.
The Standard Formula: Cell A2 to Watts
=10^((A2-30)/10) Returns linear Watts (A2 - 30) removes the +30 dB offset between milliwatts and Watts (since 1 W = 1,000 mW = 10³ mW).
10^(...) transforms the logarithmic decibel ratio back into a physical linear wattage.
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Complete RF Spreadsheet Formulas
Standardized syntax compatible with Excel 2016+, Microsoft 365, Google Sheets, and LibreOffice Calc:
| Conversion Objective | Excel / Sheets Formula | Example Input | Output Value |
|---|---|---|---|
| dBm → Watts | =10^((A2-30)/10) | A2 = 43 dBm | 19.95 W (~20W) |
| dBm → Milliwatts (mW) | =10^(A2/10) | A2 = 23 dBm | 199.5 mW (~200mW) |
| Watts → dBm | =10*LOG10(A2)+30 | A2 = 100 W | +50.0 dBm |
| Milliwatts (mW) → dBm | =10*LOG10(A2) | A2 = 1 mW | 0.0 dBm |
| dBm → RMS Voltage (50 Ω) | =SQRT(10^((A2-30)/10)*50) | A2 = 0 dBm | 0.2236 V (223.6 mV) |
| dBm → dBµV (50 Ω) | =A2+107 | A2 = -73 dBm | 34.0 dBµV (S9) |
| Negative dBm → Microwatts (µW) | =10^(A2/10)*1000 | A2 = -30 dBm | 1.0 µW |
Spreadsheet Power Conversion Questions
What is the exact Excel formula for converting dBm to Watts?
Assuming the dBm value is stored in cell A2, the formula is: =10^((A2-30)/10). For example, if A2 contains 30, the formula returns exactly 1 (Watt).
What is the Excel formula for converting Watts to dBm?
Assuming power in Watts is in cell A2, the formula is: =10*LOG10(A2)+30. For example, if A2 contains 1, the formula returns 30 (dBm).
How do you convert dBm to milliwatts (mW) in Excel?
Because 0 dBm = 1 mW, you do not need the −30 offset: =10^(A2/10). For +20 dBm, the formula returns 100 mW.
How do you convert an entire column in Google Sheets?
In Google Sheets, place this formula in cell B2: =ARRAYFORMULA(IF(ISBLANK(A2:A), "", 10^((A2:A-30)/10))). It will automatically populate all rows.
Why does my Excel formula return #NUM! or #VALUE!?
A #NUM! error occurs in the reverse calculation (LOG10) if your Watt value is zero or negative, because the logarithm of non-positive numbers is undefined. Wrap it with an IFERROR: =IFERROR(10*LOG10(A2)+30, "N/A").