petawatt
An SI unit of power equal to 10¹⁵ watts. Symbol: PW. An amount of power much larger than all the power generated by all power stations on Earth. (Consuming 1 petawatt during a duration of 1 hour would consume 1 petawatt-hour of energy.)
petawatt: a quadrillion watts, mostly theoretical
A petawatt (PW) is 1015 watts, or one quadrillion watts. To put this in scale: global electrical generation capacity sits around 8,000 gigawatts, meaning a single petawatt is roughly 125,000 times larger than all the power plants on Earth can produce simultaneously. The unit exists in metrology because laser systems and particle accelerators can briefly generate peak power in the petawatt range, even though they deliver this power for only femtoseconds or picoseconds at a time.
The petawatt appears almost exclusively in high-energy physics and advanced photonics research. Modern petawatt-class laser facilities, such as those using chirped pulse amplification (CPA) technology, compress extremely energetic pulses into incredibly short durations. A laser delivering 1 petawatt for 1 femtosecond transfers 1 joule of energy. Because the pulse duration is so brief, the total energy deposited remains modest compared to what the instantaneous power number suggests. This distinction between peak power and total energy matters enormously when discussing these systems.
Why the terminology matters
Confusion between peak instantaneous power and average power, or between power and energy, is common when discussing petawatt systems. A researcher stating that their laser achieves 1 petawatt is describing its instantaneous power at the peak of the pulse, not its continuous output. The facility's actual electrical consumption may be only megawatts, with most energy lost as heat in the amplification and cooling systems. Trade literature and equipment specifications must therefore always specify pulse duration, repetition rate, and efficiency alongside power figures.
The petawatt sits at the extreme upper end of the SI power scale. Above it lies the exawatt (1018 W), which has no known practical application. Below lies the terawatt (1012 W), used for estimating power densities in fusion experiments and modeling global energy flows. Understanding where a given measurement falls on this spectrum, and whether it represents peak, average, or instantaneous power, determines whether the number is physically meaningful or merely a large number.