Abstract: Quantitative colorimetric carbon dioxide measurement and measurement systems and methods are disclosed. The methods can include methods for calibrating a chemical colorimetric indicator used in the quantitative colorimetric carbon dioxide measurement system. Apparatuses are disclosed including a cartridge comprising a chemical colorimetric indicator that is configured to removably engage with a quantitative colorimetric measurement system. Cartridges containing a sealed container comprising a reference gas with a known concentration of carbon dioxide are also disclosed. Systems and methods for humidifying the chemical colorimetric indicator are also provided. Methods for using the systems are also disclosed including providing a breathing therapy to a patient or user.