19 inch thighs are slim because they're around 2-3 inches smaller than average. This is based on actual US data conducted on over 4,000 women and 4,000 men, which we've referenced in our other articles (see below).
Of course, you need to understand how to measure your thighs correctly if you want to get a reliable measurement.
If the bottom of your thigh (near your knee) measures 19 inches, then that's a bit bigger than average. If, however, your mid or upper thigh is 19 inches, then that's an indication that you definitely have slim thighs.
See How Your Thighs Compare:
How big are 19 inch thighs for a woman?
For a woman, 19 inch thighs are 2-3 inches smaller than average. They're certainly not big by any kind of reliable standard.
Of course, the taller that you are, the thinner that your 19″ thighs will look. This is because when you have longer thigh bones, your muscle mass and fat tissue are spread over a larger surface area.
Conversely, when you have short femurs (thigh bones), the muscle and fat are more bunched up, which gives your thighs a bulkier appearance.
Still, 19 inch thighs will look slim on just about any kind of adult female body. The only women who typically have thighs that are smaller than 19 inches are elderly women. This is because you naturally lose muscle mass as you age (a process known as sarcopenia), which reduces the circumference of your legs.
Are 19 inch thighs normal for a man?
If you're short, let's say 5'5″ and under, then 19 inch legs may look relatively normal (i.e., not skinny) on your body.
However, if you're taller, then it's likely that your 19 in thighs will look pretty thin. Whether this look is desirable or not comes down to the appearance that you're trying to achieve.
If you want to wear skinny jeans, then 19 inch and 19.5 inch thighs are conducive to that kind of appearance. But if you want to look like you work out, then your legs could do with another 2-3 inches on them because 19 inch quads aren't exactly what you'd call big.
Having 19″ thighs as a man is only bad for your health when it's indicative of you being underweight.
It's also true that men tend to store less fat on their legs than women. So you may well have equivalent levels of muscle mass to various women while still registering a smaller circumference measurement due to having less thigh fat.
How can you increase the size of your 19 inch legs?
If you've got 19 inch legs without any training, then you'll see quick gains from following a basic weight training routine.
Proven exercises like squats and Romanian deadlifts will reliably build mass on your 19 inch quads while not holding you hostage to any special machine (every gym has squat racks and barbells).
After your heavy compound lifts, you can do leg extensions and leg curls to work your quadriceps and hamstrings with extra volume. The hamstrings especially are an often-overlooked muscle group that can really increase the size of your thighs when well-developed.
On the diet side of things, make sure to eat enough protein, especially before and after your workouts. Try and get at least 40g of protein per meal, as this amount of protein has been shown to be more effective for stimulating muscle growth than 20g. 
Also, make sure to consume enough carbohydrates to fuel your leg-building workouts. Registered dietitian Paul Salter recommends eating between 0.25-0.5 grams of carbs per pound of bodyweight 3-4 hours before you hit the gym. 
Is it okay to make your 19 inch legs slimmer?
While many people wish that their legs were model-level slim, you need to understand that your thighs are already slim if they're 19 inches.
Many successful models have 19 inch thighs, for example.
Yet, even if your thighs are a few inches larger than this, they're by no means too big.
Some research even shows that those with smaller thighs have an increased risk of mortality than those with larger thighs. 
So if you have a healthy BMI and 19 inch legs, then you certainly don't need to make your thighs any smaller.
Conclusion: Is it fine to have a 19 inch thigh circumference?
Having a 19 inch thigh circumference is only bad if it's a sign that you're underweight.
Of course, some people naturally have slimmer thighs than others—even at the same height and bodyweight—because we're all built differently.
Many men, for example, store relatively little body fat on their legs but far more around their waist. For women, it tends to be the opposite; the thighs store most of their fat while the midsection stays relatively lean.
On the other hand, if you're currently overweight and want to get 19 inch thighs, then you can do so by expending more energy than you consume. Just note that most people don't need to have 19 inch legs in order to be healthy and look great.
- Macnaughton, L. S., Wardle, S. L., Witard, O. C., McGlory, C., Hamilton, D. L., Jeromson, S., Lawrence, C. E., Wallis, G. A., & Tipton, K. D. (2016). The response of muscle protein synthesis following whole-body resistance exercise is greater following 40 g than 20 g of ingested whey protein. Physiological Reports, 4(15), e12893. https://doi.org/10.14814/phy2.12893
- Salter, P. (2020, August 17). Time Your Carbs Perfectly To Crush Your Goals. Bodybuilding.Com. https://www.bodybuilding.com/fun/time-your-carbs-perfectly-to-crush-your-goals
- Kawamoto, R., Kikuchi, A., Akase, T., Ninomiya, D., & Kumagi, T. (2021). Thigh circumference and handgrip strength are significantly associated with all-cause mortality: findings from a study on Japanese community-dwelling persons. European Geriatric Medicine, 12(6), 1191–1200. https://doi.org/10.1007/s41999-021-00515-2