What's more, GPs are only marginally better at determining the weight of their patients.
The study of 1600 people published in the Australian and New Zealand Journal of Public Health asked adults across the weight ranges whether they believed they were a normal weight.
How Do I Tell If I'm Overweight?
The Body Mass Index is an objective way of determining whether you're in the healthy weight range or otherwise.
It's calculated by dividing your weight in kilograms by your height in metres squared.
The BMI isn't applicable for children, the elderly people, pregnant women and some races, but there are other ways of determining your weight range, like taking specific measurements.
Overweight and obese women were most likely to be aware of their weight range as well as men and women aged 45–64.
GPs could correctly identify their overweight patients 60.8 percent of the time, but underestimated 35.7 percent as being a normal weight.
As for obese patients, GPs got it right 60 percent of the time and incorrectly categorised 37 percent as overweight and 3 percent as normal.
The study authors concluded more needed to be done to help people recognise their own weight.
"Improvement in recognition of overweight and obesity may increase management and encourage early intervention to prevent disease associated with these weight problems," the study said.