Shopping for sex toys is easier when you know what to look for, but some of the most useful details aren't always obvious. They're often things people discover through trial and error, or after buying a product that wasn't quite what they expected.
Take lubricants, for example. In our previous article, How to Choose the Right Lubricant for Your Sex Toy, we explained why silicone lubricants aren't compatible with certain silicone toys. Using the wrong combination can damage the material, sometimes leaving the surface sticky or causing it to deteriorate. It's a simple detail, but one that's easy to overlook if you don't know to check.
Dildo sizing has its own details worth knowing before you buy. A dildo advertised as 8 inches long might have only 6 inches of insertable length. And when one manufacturer lists a diameter of 1.5 inches while another advertises a girth of 4.7 inches, they're describing roughly the same thickness.
In this guide, we'll look at what research tells us about popular dildo sizes, explain how length and girth are measured, and cover the differences in shape and firmness that can matter when choosing a dildo. By understanding these details, you'll be better equipped to compare products and find the size you're looking for.
In This Guide
What's the Most Popular Dildo Size?
With so many sizes available, it's natural to wonder what other people are buying. Are 6-inch dildos the most common? Do shoppers prefer something larger? And how much attention should you pay to the size of a bestselling toy?
There have been a few studies looking at dildo dimensions, and the findings provide some interesting reference points.
A 2017 study published in The Journal of Sexual Medicine examined realistic dildos identified as bestsellers by major online retailers. The products in the sample had an average insertable length of approximately 6.6 inches and an average circumference of 5 inches.
For comparison, a 5-inch circumference works out to a diameter of roughly 1.6 inches for a round shaft.
An earlier study from 2015 examined dildos and insertable vibrators listed across eight online retailers. Researchers found that many products were between 4 and 6 inches long, with circumferences between 4 and 5 inches.
There's an important difference between these findings. The 2017 study focused on selected bestselling realistic dildos, while the 2015 study looked at a broader selection of toys available for purchase. Neither establishes one universally preferred size.
Still, these figures are useful when comparing products. They give some context to measurements that might otherwise be difficult to judge, particularly if you're buying your first dildo.
Research references: 2017 study of bestselling realistic dildos and 2015 study of commonly sold sex toy dimensions.
Understanding Dildo Length: Overall vs. Insertable
A dildo advertised as 8 inches long doesn't necessarily have 8 inches available for penetration. Depending on the design, the base may account for a considerable portion of its overall length.
Manufacturers usually describe length in two ways, and knowing the difference can prevent a disappointing purchase.
Overall Length
Overall length measures the entire dildo from end to end. This includes the shaft, base, suction cup, or any decorative details.
Take an 8-inch realistic dildo with a detailed base and testicles. The entire product measures 8 inches, but part of that measurement comes from the base rather than the insertable shaft.
The same applies to suction cup dildos. The suction cup contributes to the overall length, even though it isn't intended for insertion.
Insertable Length
Insertable length refers specifically to the portion of the dildo designed for penetration.
Two dildos might both measure 8 inches overall, but one could have 6 inches of insertable length while the other offers 7 inches.
That's a noticeable difference, particularly when you're comparing products that look similar in photographs.
If you're shopping for an insertable toy, this is usually the more useful measurement. And if a product only provides overall length, it's worth checking whether the manufacturer gives a separate insertable measurement elsewhere in the description.
Dildo Diameter vs. Girth: What's the Difference?
Here's another detail that can make comparing dildo sizes confusing. One manufacturer might advertise a dildo as 1.5 inches in diameter, while another lists a girth of 4.7 inches.
Those numbers sound quite different, but they're describing approximately the same thickness.
Diameter measures straight across the shaft. Girth, also called circumference, measures all the way around it.
For a round shaft, multiply the diameter by approximately 3.14 to calculate girth.
| Diameter | Approximate Girth |
|---|---|
| 1 inch | 3.1 inches |
| 1.25 inches | 3.9 inches |
| 1.5 inches | 4.7 inches |
| 1.75 inches | 5.5 inches |
| 2 inches | 6.3 inches |
These conversions apply to round shafts. Dildos with irregular shapes, pronounced textures, or oval sections may measure differently.
You'll also want to check whether the listed diameter refers to the thickest part of the toy or the main shaft.
For example, a realistic dildo might have a maximum diameter of 1.75 inches at the head but measure only 1.5 inches along most of the shaft. If you only look at the maximum measurement, you won't get the full picture of its proportions.
Does Dildo Girth Matter More Than Length?
Length usually gets the most attention in product names, but girth deserves just as much consideration when you're choosing a dildo.
A longer dildo doesn't necessarily have to be inserted to its full length. You can control the depth of penetration, provided you're using the toy as intended.
Thickness is a different consideration because it determines how much space the shaft occupies during insertion.
Compare a dildo measuring 1.25 inches in diameter with one measuring 1.75 inches. There's only half an inch between them when measured straight across, but their circumferences are approximately 3.9 inches and 5.5 inches.
That's more than an inch and a half of difference in girth.
You'll also find plenty of long, slim dildos and shorter models with thicker shafts. Length doesn't automatically tell you anything about thickness.
If you've used a dildo before and want to try a different size, compare both measurements with what you already own. That gives you a more useful reference than simply choosing a product labeled large or extra-large.
What Size Dildo Should a Beginner Choose?
For a first dildo, a smaller, slimmer design is generally a more manageable starting point than something especially large or thick.
That doesn't mean there's one specific measurement every beginner should buy. People have different levels of experience with penetration, and comfort isn't determined by size alone.
A dildo with a gradually tapered tip may be easier to introduce than one with a wide, pronounced head. Likewise, a toy with some flexibility behaves differently from a rigid design.
If you're comparing a few options, pay particular attention to diameter and how the shaft changes in width.
You may also want to consider a shorter insertable length, especially if you prefer a compact toy that's easy to handle.
Use suitable lubricant, take your time, and never force insertion or continue if something is painful.
And don't feel you need to buy a larger dildo just because you've gained experience. Some people prefer slimmer designs, while others are interested in larger sizes. There's no progression you're expected to follow.
How Dildo Shape Affects Sizing
Size charts tell you how long and thick a dildo is, but shape explains how those measurements are distributed along the toy.
Two products can have the same insertable length and maximum diameter yet look very different when placed side by side.
Straight Dildos
Straight dildos usually have a relatively even shaft, although the head and base may be different widths.
Some have completely smooth surfaces, while others include realistic anatomical details or raised textures.
When comparing straight designs, check whether the listed diameter applies to most of the shaft or just its widest point.
Curved Dildos
Curved dildos have a shaft that bends or angles toward one side. Some curves are subtle, while others are much more pronounced.
These designs are sometimes made to direct pressure toward particular internal areas, depending on their intended use.
The curve changes how the toy is positioned, even if its listed length and diameter match a straight dildo.
Side-profile photos are especially useful here because they show the shape more clearly than a front-facing product image.
Tapered Dildos
A tapered dildo starts narrower near the tip and becomes wider farther down the shaft.
The increase in width may be gradual, or the toy might reach its maximum diameter relatively quickly.
For example, two tapered dildos may both have a maximum diameter of 1.75 inches. One might reach that width gradually over several inches, while the other becomes wider much closer to the tip.
The advertised maximum diameter is identical, but the actual shapes are different.
Realistic Dildos
Realistic dildos are designed to resemble a penis, often with a defined head, raised veins, and other anatomical details.
Some models have subtle textures and fairly even shafts. Others have pronounced heads, deeper surface details, or noticeable changes in thickness.
The label realistic doesn't tell you the size or firmness of the product, either. You'll find realistic dildos in slim, medium, and large designs, made from different materials and levels of firmness.
When comparing realistic models, look closely at the head and shaft dimensions rather than relying on the overall length in the product name.
Does Dildo Material Matter When Choosing Size?
Measurements are easier to interpret when you also know what the dildo is made from.
Silicone is a common material, but silicone dildos aren't all equally soft or flexible.
Some have shafts that bend easily, while others are made with a much firmer construction. You'll also find dual-density designs, which typically combine a softer outer layer with a firmer inner core.
With silicone dildos, look for information about flexibility and firmness alongside the measurements. A product described as silicone isn't necessarily soft throughout.
Glass and stainless steel dildos are different because they're rigid. They maintain their shape rather than bending or compressing like softer silicone models.
This is useful to know when comparing two dildos of the same dimensions. Identical measurements don't mean identical construction.
If the manufacturer provides a demonstration video showing how much a dildo bends, that can be particularly helpful when shopping online.
How to Compare Dildo Sizes When Shopping Online
Product photos are great for seeing colors, textures, and general design, but they're not always reliable for judging actual size.
A dildo photographed on its own can look considerably larger or smaller than expected, especially when there's nothing nearby to show scale.
Start with the measurements, then compare the features that aren't always obvious in the photos.
- Insertable length: Check how much of the shaft is intended for penetration, rather than relying on the overall length.
- Diameter or girth: Make sure you're comparing the same type of measurement, and check whether it refers to the widest point.
- Shape: Look at the shaft from different angles. A curved, tapered, or realistic design may have changing proportions.
- Firmness: Find out whether the toy is flexible, firm, rigid, or made with dual-density construction.
- Base: Check for a suction cup, flat base, or other features that affect the overall dimensions and intended use.
If you're unsure how big a dildo will be in person, a ruler or measuring tape can help you picture the measurements.
And if you already have a toy you're comfortable using, compare its dimensions with the one you're considering. Even when the shape is different, those numbers give you a familiar starting point.
For anal insertion, make sure the product is specifically designed for anal use and has a secure, flared base or another appropriate safety feature. A dildo intended for vaginal use isn't automatically safe for anal insertion.
With the measurements and product details in hand, you can compare dildo sizes and styles without relying entirely on pictures or vague descriptions such as medium, large, or realistic.
Frequently Asked Questions About Dildo Sizes
What's the most popular dildo size?
A 2017 study of selected bestselling realistic dildos found an average insertable length of approximately 6.6 inches and an average circumference of 5 inches. These figures describe a sample of products, not one universally preferred size.
What is a good dildo size for beginners?
A smaller, slimmer dildo is generally a practical starting point. Consider the insertable length, diameter, shaft shape, and firmness. There's no single size that suits every beginner.
Is dildo girth the same as diameter?
No. Diameter measures straight across the shaft, while girth measures around it. For a round shaft, multiplying the diameter by approximately 3.14 gives you the circumference.
Does dildo length include the base?
Overall length includes the entire toy, including the base. Insertable length measures only the part intended for penetration. Always check which measurement the manufacturer provides.
Are longer dildos always thicker?
No. Length and thickness vary independently. You can find long, slim dildos as well as shorter models with wider shafts.
Are silicone dildos always flexible?
No. Some silicone dildos are very flexible, while others are quite firm. Dual-density models usually have a softer exterior and firmer core, although their construction varies.
Can two dildos with the same diameter have different shapes?
Yes. Maximum diameter only tells you the widest measurement. Curved shafts, tapered tips, pronounced heads, and realistic textures can all change the proportions of a dildo.
Choosing the Right Dildo Size
The research on commonly sold and bestselling dildos gives us a useful reference, but it doesn't mean everyone should choose the same length or girth.
When comparing products, start with the insertable length and diameter. Then look at the shape and how the shaft changes in width. Material and firmness are also worth checking, particularly when comparing silicone with more rigid designs.
These are the details that make dildo sizing easier to understand. And once you know what the measurements mean, you can spend less time guessing from product photos and more time finding a toy with the features you're looking for.