The muscles in the biceps—the long head and the short head—as well as those in the triceps, grow in strength and size as children develop.
As such, the ideal biceps size depends on your (or your child’s) height, weight, gender, and age.
This article discusses whether having 6 inch arms, 7 inch arms, and 8 inch arms is something that you should be concerned about.
Are 8 inch arms small?
Whether or not 8 inch arms are small depends on the factors mentioned above; age, height, weight, and gender.
For boys and girls between the ages of 7 and 9, 8 inch biceps and 8.5 inch biceps are completely normal (at this young age, gender doesn’t have much influence on arm size). 
7 inch biceps and 7.5 inch biceps are typical for children aged 4-6.
6 inch arms and 6.5 inch arms are commonly observed in children who are between the ages of 1 and 3.
Now, if you still have 8 inch arms during adolescence and adulthood, then that’s a strong sign that you’re severely underweight and should talk to your doctor.
Why do some people have 8 inch biceps?
Children naturally go through stages of having 6, 7, and 8 inch biceps as they grow and develop.
If a teenager or young adult has such an arm size, then it could be because they’re performing excessive amounts of physical activity (particularly endurance exercise) and/or not consuming enough calories.
Individuals with body image issues may have an 8 inch bicep size for similar reasons. 
So if you’re a teenager or adult with 8” biceps, make sure to talk with your doctor so that they can help you to increase your body mass in a safe and effective manner.
If you’re the parent of a child with 8” arms, then you can check the chart above to see if their arms are a normal size or not.
How can you increase your 8 inch arms naturally?
People who want to grow their arms typically begin by increasing their calories intake and starting a basic resistance training program.
Eating in a calorie surplus and consuming adequate protein will help your body to create new muscle tissue. It’s likely that you’ll also gain some fat, which is completely normal and will likely be beneficial if your starting point is really skinny.
Performing strength training helps to ensure that some of the calories that you do consume get partitioned towards muscle growth rather than pure fat storage.
While it might be tempting to forgo exercise altogether when you’re trying to gain weight, your arms will look much better if they have some muscle on them.
6 inch arms, 7 inch arms, and 8 inch arms can all be standard circumference measurements for children. The above chart will help you to see how your child’s arms compare to those of the average boy and girl.
Now, if you have any of the aforementioned measurements as a teenager or adult, then that’s likely a sign that you have an underweight BMI and should talk to your physician. 
- Fryar CD, Gu Q, Ogden CL. Anthropometric reference data for children and adults: United States, 2007–2010. National Center for Health Statistics. Vital Health Stat 11(252). 2012.
- Hijji, T. M., Saleheen, H., & AlBuhairan, F. S. (2021). Underweight, body image, and weight loss measures among adolescents in Saudi Arabia: is it a fad or is there more going on? International Journal of Pediatrics and Adolescent Medicine, 8(1), 18–24. https://doi.org/10.1016/j.ijpam.2020.01.002
- NHS website. (2021a, November 18). How can I gain weight safely? Nhs.Uk. https://www.nhs.uk/common-health-questions/food-and-diet/how-can-i-gain-weight-safely/