A guide to picking the right tampon size for your period

• Tampons sizes correspond to flow absorption, rather than the size of the tampon itself.
• The absorbency of different sizes are: light (3mL), regular (5mL), and super (12mL).
• It's always best to choose the lightest tampon size that works for your flow.

If you're new to tampons, you may not know how to choose the right size for your flow. There are many important factors to consider when choosing a tampon size - you may need more or less absorbent tampons depending on how active you are or where you are in your cycle.

Here's how to know when you should use light, regular, or supersize tampons.

Different tampon sizes

"Some women may not realize but the tampon size actually corresponds to the amount of flow absorption rather than the actual size of the tampon itself," says Jennifer Wider, MD, a medical advisor for the Society for Women's Health Research.

This means that light tampons are a similar length - about two inches long - but are slightly slimmer and can't absorb as much fluid as regular or super tampons. In general, the absorbency sizes are:

Some brands may offer even more absorbent sizes like super plus, which hold 15 ml and ultra, which hold up to 18 ml.

How to pick the best tampon size for you

If you don't know which tampon size to choose, trial and error may be your best bet, says Christine Greves, MD, an OB-GYN at Winnie Palmer Hospital.

Medical term: A heavy flow is defined in a couple of ways: It can either refer to losing 80 ml or more of blood during a period, or having periods that last longer than seven days, or both. If you have a heavy flow, you should get a blood test for iron deficiency anemia.

However, it's best to start with whichever size you think corresponds to your flow. So if you think you have a lighter flow, choose a light size, but if you think you have a heavier flow, stick to regular to start.

If whichever tampon you choose doesn't leak any blood for four to six hours, you've most likely chosen the right size, Greves says. If not, size up. If a lot of white is still showing after six hours, you may be able to size down.

It's always best to choose the lightest tampon size that works for you, because higher absorbency tampons carry a higher risk of a serious and potentially deadly infection called toxic shock syndrome.

Note: Toxic shock syndrome (TSS) is rare affecting about 0.0035% of the US population. Symptoms of TSS include sudden fever, low blood pressure, vomiting, confusion, and more. Seek immediate medical aid if you think you may have TSS.

What to keep in mind when choosing a tampon

• If you're new to tampons: Start with a low absorbency tampon, like a light tampon ora junior size made for teenagers. Because they're slimmer, they're easier to insert for beginners, Wider says.
• If your flow changes throughout your cycle: Often, the first two days of your period are the heaviest, so start with more absorbent tampons and then use a less absorbent size towards the end, Wider says.
• If you're active. Exercising increases the risk of leaks, so consider 'active tampons' that expand to cover more surface area. However, regular tampons may also work fine, Wider says.

Insider's takeaway

Tampon sizes vary based on how much they absorb, and you can choose which size is best for you based on the lightness or heaviness of your flow.

Moreover, you should always use a tampon that's absorbent enough to prevent leaks, but also choose the lowest absorbency that works for your period.

"Everyone is different, it's important to know your body and choose products based on comfort level and what works best for you," says Wider.

If you're having a hard time finding the right size, or your flow is too heavy for super size tampons, reach out to your OB-GYN who can help.