Dildos & strap-ons
Dildo size guide: the number on the box is the wrong number
Three different measurements get called "size" in this category, and the one listings publish is the least useful of the three.
A listing usually gives a total length and a diameter. Neither is what you need. Total length includes a base you cannot insert, and diameter is a measure of a circle that a cross-section is not, because most of these toys are slightly oval and many have a head wider than the shaft.
The two figures that predict comfort are insertable length and circumference at the widest point. Insertable length is total length minus the base and any flare. Circumference is the one you can measure on something you already own with a piece of string, and the one almost nobody publishes.
Diameter to circumference, so a listing can be converted
| Diameter | Circumference | Usually described as |
|---|---|---|
| 25 mm (1.0 in) | 79 mm (3.1 in) | Slim, beginner, or a training size |
| 32 mm (1.25 in) | 101 mm (4.0 in) | Slim to average |
| 38 mm (1.5 in) | 119 mm (4.7 in) | Average, the most common size sold |
| 44 mm (1.75 in) | 138 mm (5.4 in) | Thick, or girthy |
| 51 mm (2.0 in) | 160 mm (6.3 in) | Large |
| 64 mm (2.5 in) | 201 mm (7.9 in) | Extra large, and a size to work up to |
Measuring what you already own, which is the only reliable baseline
Insertable length, with a ruler against the shaft
From the tip to where the base or flare begins, not to the bottom of the base. This is the number that differs most from the figure on the box, sometimes by two or three centimeters.
Circumference, with a strip of paper
Wrap a strip around the widest point, mark where it meets, lay it flat against a ruler. A tape measure works too. This takes ten seconds and tells you more than any listing.
Note where the widest point is
A toy that is widest at the head behaves completely differently from one that is widest at the base, even at the same circumference. The first is hardest at the start, the second at the end.
Write both numbers down
Once you know the insertable length and circumference of something that works, every future purchase becomes arithmetic instead of guesswork. This is the single most useful thing in this guide.
What the published numbers hide
- Firmness changes effective size. A soft dual-density toy at 44 mm compresses and inserts more easily than a rigid silicone one at 38 mm. Shore hardness is published occasionally; when it is not, "dual density" or "squishy" in the description is the clue.
- Shape matters as much as girth. A gradual taper distributes the stretch over distance. An abrupt shoulder concentrates it at one point, and that point is where discomfort happens.
- Curve changes usable length. A strongly curved toy has less effective insertable length than a straight one of the same measurement, because the curve does not follow a straight path.
- Base width is not girth. A wide flared base is a safety feature and a harness feature. It is not part of what goes in, and it should not be counted in either number.
- Anal and vaginal sizing are not the same scale. Anal tissue does not accommodate girth the way vaginal tissue does, and the limiting factor is the rate of change rather than the final number. A size that is unremarkable vaginally can be a project anally.
Questions people ask
- Is length or girth more important?
- Girth, for comfort. Length mostly determines whether a toy can reach something and whether it is unwieldy. Almost every report of a toy being too much is about circumference, not centimeters of length.
- Why does a listed diameter feel bigger than expected?
- Because a diameter describes a circle and the stretch you feel follows the circumference, which is about three times the diameter. A one-centimeter jump in diameter is a three-centimeter jump in the measurement your body is responding to.
- What size should a first dildo be?
- Smaller than the thing you would pick from a photograph. A listing around 30 to 35 mm diameter, soft, with a gradual taper, leaves room to go up later. A large first purchase is the commonest reason a toy ends up unused.
- How do I compare a toy to a partner?
- Measure the circumference of both with the same strip of paper. It is the only comparison that works, and it works better than any description either of you would give.