Measuring a penis involves determining its length and girth. A condom that's too small can be uncomfortable, and one that's too loose can come off prematurely. The best way to make sure the condoms you purchase for yourself or your loved one fit is to get an accurate measurement of the penis.

Assumptions about penis size from finger length, foot size, and height are not supported by research.﻿﻿ The only way to get accurate numbers for fitting a condom is to measure the penis while it's erect.

Also, note that penis size can vary due to stress, fatigue, frequency of sexual activity, and level of arousal, so you may want to do several measurements at different times throughout the day, over several days. From that starting point, use the following guidelines for getting the length, girth, and width.

Verywell / JR Bee

Measuring Penis Length

Start by measuring the length of your penis:﻿﻿

Position a ruler or measuring tape at the base of the erect penis, where it attaches to the body. Press into the pubic bone as far as you can, until you contact the bone. This is especially important if there's a lot of belly fat. Measure from the base to the end of the tip.

The average erect penis is a little over 5 inches (13 centimeters) long.

Measuring Penis Girth

Next, measure the girth of the penis (that is, the circumference or thickness).

For this step, use a soft measuring tape or a piece of string. If you choose the latter, make sure it doesn't have any stretch. A length of yarn, for example, could introduce measurement errors. Gently wrap the tape or string one time around the thickest part of the shaft of the erect penis. Note where the ends of the tape meet; that's the number you're looking for. If you're using string, mark where the end of the string meets the rest of it, then stretch out the string and use a ruler to measure the distance from the mark to the end.

The average penis is around 4.5 inches (11.5 centimeters) in girth.﻿﻿

Measuring Penis Width

Some condoms are sized according to width or diameter. To get this measurement, first find the girth, using the method described above and divide it by 3.14.

Using Your Penis Size to Choose a Condom

Once you are confident that you have figured out your penis size, you should be able to determine what size condom you need.

If your penis is of average size, a standard size condom should provide you with an accurate fit. If yours measures larger, you may need a condom labeled "large"; if it's smaller, try a "snug" condom. Remember that when it comes to condoms, size matters: the better the fit, the better it will protect you against unwanted pregnancies and sexually transmitted infections.