He and his small team made meticulous measurements on people engaged in various forms of work, leisure and household activities. Some of these measurements were made on workers themselves (eg miners, bricklayers, lumberjacks), but others were carried out on volunteers. Either way Durnin was usually able to combine his work with pleasure. Sometimes it was of great practical value to himself and family: eg persuading students to have their energy expenditure levels measured in his garden and house while digging, hoeing and sawing trees.
Durnin was also known internationally for his work on the measurement of obesity and weight reduction. He demonstrated the pitfalls of using height and weight measurements as an indicator of obesity, and promoted the use of skinfold callipers as a more accurate measure. He compiled tables for the calculation of body fat from skinfold measurements, and these are still widely used.