Understanding cup measurements helps you find the perfect fit. Capacity, diameter, and length all work together to determine if a cup will work for your body and flow. Let's break down what those numbers really mean.

What is Cup Capacity?

Capacity is how much menstrual blood a cup can hold. It's measured in milliliters (ml) or fluid ounces (oz). Most cups hold between 15ml and 40ml when filled to the rim.

Here's what you need to know:

Small cups: usually 15-25ml
Medium cups: usually 25-30ml
Large cups: usually 30-40ml

Many cups have marks on the side showing you how much they hold. These lines help you track your flow over time.

Reading Capacity Markings

Most cups have little lines or numbers printed on the inside or outside. These show measurements in milliliters. Some cups also show ounces.

The markings usually look like this:

Bottom line: 5ml or 10ml
Middle line: 15ml or 20ml
Top line: 25ml or 30ml

Not all cups have the same markings. Some have just one line. Others have several. The markings help you see how heavy your period is on different days.

How to Use the Markings

When you empty your cup, check where the blood reaches. If it's at the 15ml line, you know you had 15ml of flow since your last change. This information helps you decide:

How often to empty your cup
Whether you need a bigger or smaller size
How your flow changes during your period

Diameter Measurements

Diameter means how wide the cup is at its widest point—usually at the rim. This measurement matters because it affects how the cup fits and seals inside you.

Common rim diameters range from 38mm to 48mm. That's about 1.5 to 2 inches wide. Here's what this means for you:

Smaller diameter: easier to insert, may work better with a low cervix
Larger diameter: may seal better, usually holds more

Women with strong pelvic floors often prefer smaller diameters. Women who've given birth vaginally often prefer larger diameters. But every body is different.

Length Measurements

Cup length is measured two ways: with the stem and without the stem. Both numbers matter.

The cup body length (without stem) usually ranges from 45mm to 60mm. The total length (with stem) can be 60mm to 75mm or more. Your cervix height determines which length works best:

Low cervix: look for shorter cups (45-50mm body length)
Average cervix: most standard cups work (50-55mm body length)
High cervix: you may need longer cups (55-60mm body length)

Remember, you can always trim the stem if a cup is too long. But you can't make a cup longer if it's too short.

How Capacity Relates to Flow

Your flow type affects which capacity you need. A light flow might only be 5-10ml per day. A heavy flow could be 30-40ml per day or more.

Here's a general guide:

Light flow: 15-20ml capacity is usually enough
Medium flow: 20-30ml capacity works well
Heavy flow: 30-40ml capacity gives you longer wear time

If you have a heavy flow, a larger capacity means fewer bathroom trips. You can wear the cup for 8-12 hours without worrying about leaks.

Why Measurements Matter

Getting the right measurements makes your cup experience so much better. A cup that's too big can be uncomfortable. A cup that's too small might leak or be hard to remove.

Measurements help you:

Match the cup to your cervix height
Choose enough capacity for your flow
Avoid discomfort from wrong sizing
Find cups that work with your body shape

Finding Your Perfect Fit

You know your body best. Start by checking your cervix height during your period. This tells you what length you need. Then think about your flow to determine capacity.

The Cup-Figurator quiz asks about your cervix height, flow, and other factors. It uses this information to recommend cups with the right measurements for you.

Understanding capacity and measurements takes the guesswork out of cup shopping. When you know what the numbers mean, you can make smart choices. The right cup size transforms your period from stressful to simple.