Whether an electric kettle is cheaper than gas depends mainly on energy prices and heating efficiency. In many situations, gas and electricity each have advantages, so the final cost can vary.
Gas is often cheaper per unit of energy than electricity in many regions. Because of this, boiling water on a gas stove can sometimes cost slightly less than using an electric kettle. For example, one comparison experiment found that boiling a cup of water cost about 0.5p using gas versus around 1.4p using an electric kettle.
Even though gas energy may be cheaper, electric kettles are usually more efficient at transferring heat to the water. The heating element sits directly in the water, so less heat is lost to the surrounding air. Electric kettles typically reach around 80% efficiency, while stovetop methods lose more heat during heating.
Electric kettles generally boil water much faster. In experiments, an electric kettle could boil a cup of water in about 1 minute, while a gas burner took around 5 minutes for the same amount.
Gas: Often cheaper per unit of energy.
Electric kettle: More efficient and faster for boiling water.
Actual cost: Depends on local electricity and gas prices.
In many households, the cost difference for a single kettle boil is very small, so people often choose electric kettles because of their speed, convenience, and automatic shut-off safety features.