The femtowatt (fW) is equal to one quadrillionth (10−15) of a watt. Technologically important powers that are measured in femtowatts are typically found in reference(s) to radio and radar receivers. For example, meaningful FM tuner performance figures for sensitivity, quieting and signal-to-noise require that the RF energy applied to the antenna input be specified. These input levels are often stated in dBf (decibels referenced to 1 femtowatt). This is 0.2739 microvolt across a 75-ohm load or 0.5477 microvolt across a 300-ohm load; the specification takes into account the RF input impedance of the tuner.
| Definition | Relation to SI units |
|---|---|
= 10-15 W |
| watt | microwatt | imperial ton of refrigeration | femtowatt | gigawatt | nanowatt | petawatt | picowatt |
|---|---|---|---|---|---|---|---|
| 1 | 1 000 000 | 0.0002539 | 1.0 × 1015 | 1.0 × 10-9 | 1 000 000 000 | 1.0 × 10-15 | 1 000 000 000 000 |
| 1.0 × 10-6 | 1 | 2.5387959760084 × 10-10 | 1 000 000 000 | 1.0 × 10-15 | 1 000 | 1.0 × 10-21 | 1 000 000 |
| 3,938.875 | 3 938 875 000 | 1 | 3.938875 × 1018 | 3.938875 × 10-6 | 3 938 875 000 000 | 3.938875 × 10-12 | 3.938875 × 1015 |
| 1.0 × 10-15 | 1.0 × 10-9 | 2.5387959760084 × 10-19 | 1 | 1.0 × 10-24 | 1.0 × 10-6 | 1.0 × 10-30 | 0.001 |
| 1 000 000 000 | 1.0 × 1015 | 253,879.5976008 | 1.0 × 1024 | 1 | 1.0 × 1018 | 1.0 × 10-6 | 1.0 × 1021 |
| 1.0 × 10-9 | 0.001 | 2.5387959760084 × 10-13 | 1 000 000 | 1.0 × 10-18 | 1 | 1.0 × 10-24 | 1 000 |
| 1.0 × 1015 | 1.0 × 1021 | 253,879,597,600.84 | 1.0 × 1030 | 1 000 000 | 1.0 × 1024 | 1 | 1.0 × 1027 |
| 1.0 × 10-12 | 1.0 × 10-6 | 2.5387959760084 × 10-16 | 1 000 | 1.0 × 10-21 | 0.001 | 1.0 × 10-27 | 1 |
| Symbol | Definition |
|---|---|
| ≡ | exactly equal |
| ≈ | approximately equal to |
| = | equal to |
| digits | indicates that digits repeat infinitely (e.g. 8.294 369 corresponds to 8.294 369 369 369 369 …) |
| 1 femtowatts | = 1.0E-15 watts |
| 2 femtowatts | = 2.0E-15 watts |
| 3 femtowatts | = 3.0E-15 watts |
| 4 femtowatts | = 4.0E-15 watts |
| 5 femtowatts | = 5.0E-15 watts |