What unit has largely replaced the BTU in many areas?

The joule is the unit that has largely replaced the British Thermal Unit (BTU) in many scientific and engineering contexts. This shift occurs because the joule is part of the International System of Units (SI), which is used globally and provides a standard method for measuring energy.

The joule is defined based on measurable physical quantities, specifically as the energy transferred when applying a force of one newton over a distance of one meter. This makes it a straightforward unit for calculations in physics, chemistry, and engineering.

In contrast, while calories are another energy unit, they are more specific to the field of nutrition and thermodynamics and are less commonly used in general physics applications than the joule. Watts and kilowatts are units of power, which measure the rate of energy transfer rather than energy itself, thus serving a different purpose in physical science.