Volcanic ash is a hazard associated with volcanoes. Knowing an ash cloud’s location is essential for minimising the hazard. This includes knowing the height. This study adapted a well-known technique for obtaining the height of meteorological clouds, known as CO₂ slicing, for volcanic ash. Modelled data were used to refine the method and then demonstrate that the technique could work for volcanic ash. It was then successfully applied to data from the Eyjafjallajökull and Grímsvötn eruptions.