The Haugh unit is a measure of egg protein quality based on the height of its egg white (albumen). The test was introduced by Raymond Haugh in 1937  and is an important industry measure of egg quality next to other measures such as shell thickness and strength.
An egg is weighed, then broken onto a flat surface (breakout method), and a micrometer used to determine the height of the thick albumen (egg white) that immediately surrounds the yolk. The height, correlated with the weight, determines the Haugh unit, or HU, rating. The higher the number, the better the quality of the egg (fresher, higher quality eggs have thicker whites). Although the measurement determines the protein content and freshness of the egg, it does not measure other important nutrient contents such as the micronutrient or vitamins present in the egg.
The formula for calculating the Haugh unit is:
- HU = Haugh unit
- h = observed height of the albumen in millimeters
- w = weight of egg in grams
- Monira, K. N.; Salahuddin and, M.; Miah, G. (2003), "Effect of Breed and Holding Period on Egg Quality Characteristics of Chicken" (PDF), International journal of Poultry Science 2 (4): 261–263
- Jeffrey Kluger (July 8, 2010). "Organic Eggs: More Expensive, but No Healthier". Time magazine. Retrieved 2010-07-11.