What size dildo should you choose? How to read the measurements

When people ask what size dildo they should choose, they usually think about length. But it’s the diameter — how thick the dildo is — that determines how it feels during insertion, and that’s where most buyers who get it wrong have miscalculated. Length matters for how deep you can go, but you decide how much of it you use. You can’t choose to ignore thickness.

The second mistake is reading the wrong length. A dildo has at least two length measurements: the total length, which counts the base, the balls, or the suction cup, and the insertable length, which is the part that can actually be inserted. The difference can be several centimeters, and the product name sometimes indicates one and sometimes the other.

If you’re unsure, start narrower and shorter than you think you need. A moderate dildo is used more often than one that feels like a challenge, and you can always move on to a larger model once you know what you think. The rest of this guide is about how you read the measurements and how you compare them across models. Do you want the full picture before your first purchase, there is 10 things to know before you buy your first dildo.

A serious manufacturer publishes multiple measurements, not just one. Here are the four you most often encounter in a specification, and what each one says.

Total length is the entire product from tip to base. The insertable length — sometimes called the insertable length — is what’s left once the base, the balls, and the suction cup have been subtracted. It’s the insertable length you should compare.

The difference varies a lot between models.Silexd Silex-D 17.6 cm is 17.6 centimeters total but only 13.6 centimeters insertable, because the balls and suction cup take up four centimeters. King Cock Elite 20 cmis 22.0 centimeters total and 20.3 centimeters insertable—there, only 1.7 centimeters are lost.

The product name isn’t a reliable guide. King Cock 15 cm is called that based on the insertable length, 15.2 centimeters, while the entire product, according to the manufacturer, is 17.4 centimeters. The Silexd model with 17.6 in the name instead indicates the overall length. Two dildos with almost the same number in the name can therefore differ by almost two centimeters in the measurement that actually matters.

The diameter is the thickness straight through, measured across the shaft. The circumference is the measurement all the way around. Manufacturers most often state the diameter, but some state the circumference, and some shops mix them up. The circumference is roughly the diameter times 3.14—so a diameter of 3.5 centimeters corresponds to about 11 centimeters in circumference. If you see a “diameter” of 11 or 12 centimeters, it’s almost certainly the circumference that’s meant.

Also check which diameter is given. Many dildos aren’t equally thick all the way along.Epic Basilisk is 4.8 centimeters at the top but 4.0 centimeters along the shaft according to the manufacturer’s size guide, and Ravager Rippled Tentacle grows from 3.0 to 4.6 centimeters. It’s the largest diameter that determines whether a dildo fits, but the smallest says something about what it’s like from the start.

Weight doesn’t affect how big a sex toy feels, but it affects how it feels to hold and how well a suction cup supports it. Silexd 17.6 cm weighs 251 grams, King Cock Elite 20 cm 511 grams. Glass dildos are heavy relative to their size—according to shop information, a 17.5-centimeter glass dildo can weigh around 470 grams.

The base diameter is rarely counted as a sizing measure, but it’s a safety measure. A base that is clearly wider than the thickest part of the shaft prevents the dildo from sliding in all the way, which is crucial for anal use. Epic Basilisk has a base of 10 centimeters compared to its thickest section of 4.8—more than twice as wide.

There’s no one size that fits everyone, but there is a safe starting point. A diameter of around 3.5 to 4 centimeters and an insertable length of 13 to 15 centimeters is about where several of the smaller models in our overviews are, and it’s enough to know what you think about it. It’s not a rule—some want it slimmer, others already know they want more.

Some models with published measurements in that class: Silexd 17.6 cm is 3.5 centimeters in diameter and 13.6 centimeters insertable. Mythology Kuno UtopiaIt is 4 centimeter and 13 centimeter. King Cock 15 cm is 4,5 centimeter and 15,2 centimeter – a little thicker, but still moderate.

Also think about the shape. A dildo that tapers toward the tip is easier to start with than one that is the same thickness all the way, because your body can get used to it gradually. A realistic dildo with a defined glans often has its greatest diameter right at the very front, which means the thickest part comes first.

Two dildos with the same diameter do not necessarily feel equally big. The material yields differently. Soft silicone compresses a bit, while glass and metal do not yield at all—so a glass dildo of 3 centimeters is therefore perceived as thicker than a silicone dildo with the same measurements. Keep that in mind when you compare it with a toy in another material.

Double density, or dual density, is a way to get both: a firm core that holds its shape and a softer outer layer. Both the Silexd and King Cock Elite models are built this way. For the size choice, that means the surface gives in a little, but the dildo does not bend out of the way.

If you’re considering glass, read are glass dildos safe? before you choose a size. Glass is non-porous and easy to keep clean, but the hardness means you should choose something slightly narrower than you would have in silicone.

There is no reason to strive to go up in size, but many want to when they know what they think of it. Then go up one size at a time. Either switch to a longer model with roughly the same diameter, or to a slightly thicker one with the same length—not both at the same time. Half a centimeter in diameter sounds like a little, but it is clearly noticeable.

Among larger models with published dimensions, King Cock Elite 20 cm has 20,3 centimeters insertable and 5,4 centimeters in diameter.Silexd Silex-D The Originalis stated to be 20 centimeters insertable and 5,4 centimeters in diameter.King Cock 23 cmgoes to 21,5 centimeters and 5,5 centimeters.

Here, it also becomes more important to check the numbers. For Silexd Original, the manufacturer prints 26,6 centimeters on the box but states 25 centimeters in its specification, and several shops state 17 centimeters insertable where the manufacturer states 20. When a shop and the manufacturer say different things, trust the manufacturer.

For anal use, it’s the same as for vaginal use — the diameter is what matters — but the margins are smaller. Choose a narrower model than you would for vaginal use, use plenty of lube, and take your time. Stop if it hurts.

The base is just as important as the size. Only use an anal dildo if it has a flared base or a flange that is clearly wider than the shaft, and if the manufacturer states that it is made for that. Mythology Kuno Utopia, for example, is explicitly intended for anal use and has a flared suction-cup base, but the manufacturer does not publish the base diameter. Epic Basilisk publishes it: 10 centimeters.

For those who want to start from the beginning, there is anal plug for beginners — a plug is often a better first step than a dildo, because it’s shorter and shaped to stay in place.

1. Reading the product name instead of the specifications. The number in the name can be total length, insertion length, or an approximate inch measurement.

2. Comparing length when it’s the diameter that matters. A full centimeter longer is felt less than half a centimeter thicker.

3. Mixing up diameter and circumference. A specification of 12 centimeters in “diameter” is almost always the circumference.

4. Buying too large because it looks small in a picture. Product images have no scale. Hold up a ruler when you read the measurements.

5. Forgetting the material. Glass and firm silicone feel bigger than soft silicone with the same measurements.

A larger dildo requires more lube, not less. Use water-based lube for silicone: silicone-based lube can damage the surface of a silicone sex toy, and several manufacturers explicitly advise against it. Glass and metal can handle all types. More about the choice is in which lube should you choose and in the comparison of lube.

Clean the dildo with lukewarm water and mild soap before and after use, and let it dry completely. Use a condom if you share it. Non-porous materials like silicone and glass can be made completely clean, while PVC can only be cleaned on the surface. The full walkthrough is in How to clean sex toys.

Do you want to compare more models with published dimensions? The guides to realistic dildos, glass dildosandfantasy dildos, and the entire range in the category of dildos.