Is there a device that lets linguists measure aspiration? I want to find out if languages in which aspiration can be the only difference between phonemes (e.g. Chinese) have more breath difference between aspirated and unaspirated consonants than, say, English. I need a unit of aspiration and a way to measure it for that purpose.
Aspiration is not a measurable quantity, it is a classification like "good". There is an acoustic measure and one or more physiological measures. The physiological measure is not DIY unless you want to spend a lot of bux to get the equipment. For the record, you can measure airflow, where aspirated consonants are predicted to have greater airflow. You need an airflow mask (plus transducers, and calibration gadgetry), and I don't know what they cost these days but expect at least $1,000 for the mask alone.
The alternative is to measure Voice Onset Time from ordinary voice recordings, which requires a computer and microphone, plus free software (Praat). The first step is to record e.g. "tank" and "dank", then using Praat (downloading and reading the basic "how to use" readings), open the two sound files; then learn how to identify / separate the vowel from the preceding consonant, according to certain acoustic landmarks. VOT is the time from the onset of vocal fold vibration to the release of the stop. In "tank", there is a large positive lag between the release of the stop and the beginning of vocal fold vibrations, and in "dank" there is a small lag or even a negative lag (vocal fold vibration starts before the release of the stop). This article (if you can access it) is an informative comparative study of a number of languages with aspirated and non-aspirated consonants where you can see how languages differ in the VOT associated with aspirated and non-aspirated stops.