Dildo girth is the distance all the way around the shaft at its widest point. Diameter is the distance straight across. Divide girth by 3.14 to get diameter, or multiply diameter by 3.14 to get girth. Most product listings quote diameter, most people describe what they want in girth, and that mismatch is why so many toys arrive wider or narrower than expected.
TL;DR
- Girth is circumference, the measurement around. Diameter is the measurement across.
- Girth divided by 3.14 gives diameter. Diameter times 3.14 gives girth.
- A 2 inch diameter dildo is about 6.3 inches around.
- Anything past roughly 1.75 inches across reads as genuinely girthy to most people.
- Measure at the thickest point, not the average, since that is the part you have to accommodate.
Girth and Diameter Are Not the Same Number
This is the single most common mix-up in dildo sizing. Girth is circumference, the loop around the outside. Diameter is the straight line across the middle.
They describe the same thickness, but the numbers look completely different. A dildo that is 1.5 inches across is 4.7 inches around. Someone reading 4.7 inches without context might picture something much bigger than it is.
When a listing says 2 inch dildo and means width, it is nearly always diameter. When a person says they want 6 inch girth, they mean circumference.
How to Measure Girth on a Dildo You Own
- Find the thickest part of the shaft. On most realistic dildos this sits about a third of the way up from the base.
- Wrap a soft tailor's tape around it, snug but not compressing the silicone.
- Read the number where the tape meets. That is girth.
- No tape measure? Wrap a strip of paper or a shoelace around, mark where it overlaps, then lay it flat against a ruler.
How to Measure Diameter
Lay the dildo on a flat surface and measure straight across the widest point with a ruler. If you want to be precise, stand a book upright on each side of the shaft and measure between the books, which avoids the parallax error you get eyeballing a curved surface against a ruler.
Converting Between the Two
The conversion is just pi. Diameter to girth, multiply by 3.14. Girth to diameter, divide by 3.14.
- 1.25 inches across = about 3.9 inches around (slim)
- 1.5 inches across = about 4.7 inches around (average realistic)
- 1.75 inches across = about 5.5 inches around (entering girthy)
- 2 inches across = about 6.3 inches around (solidly girthy)
- 2.5 inches across = about 7.9 inches around (extra girthy)
- 3 inches across = about 9.4 inches around (extreme)
What the Numbers Actually Feel Like
Numbers on a page do not tell you much until you anchor them to something. A standard soda can is about 2.6 inches across. A D battery is about 1.3 inches. A wine cork is roughly 0.9 inches.
Hold one of those and you have a far better sense of a listed diameter than any product photo will give you. This matters because girth, unlike length, cannot be worked around by adjusting angle or depth. You either accommodate the width or you do not.
Published research has catalogued the dimensions of commonly sold sex toys precisely because clinicians recommending them had no reliable size data to work from (Herbenick et al., The Journal of Sexual Medicine, 2015). Product listings remain inconsistent, so measuring yourself is still the only reliable method.
Why Listings Disagree With Each Other
Three things vary between brands. Some measure at the very widest bulge, some measure mid-shaft. Some include the flare of the head, some do not. Soft dual-density toys compress under a tape measure, so the same toy can read differently depending on how hard the tape was pulled.
Treat a listed measurement as approximate. If the difference between 1.75 and 2 inches matters to you, look for a listing that states where it measured. Our dual density guide explains why soft-layer toys are the hardest to measure consistently.
Using Girth to Pick a Harness
If you are wearing the toy, base diameter is what matters, not shaft diameter. The base is what passes through the O-ring. Measure straight across the base just above the flare, then pick a ring that size or one step smaller. Our strap-on harnesses page has the full sizing walkthrough.
Frequently Asked Questions
Is girth or circumference the correct term?
They mean the same thing when talking about dildos. Girth is the everyday word, circumference is the geometric one. Both refer to the measurement around the shaft rather than across it.
What counts as a girthy dildo?
There is no official threshold, but most people use girthy for anything past about 1.75 inches in diameter, which is roughly 5.5 inches around. Below that reads as average or slim.
Should I measure my own body to work out what fits?
You cannot usefully measure internal width, since the tissue is elastic and changes with arousal. A better method is to start with something you know is comfortable, measure that, and use it as your baseline when sizing up.
Written by Casey M., Resident Toy Specialist at Epic Dildos. Updated September 2026.
Ready to shop by width? Browse girthy dildos, or read the full thick dildo guide. For body-safe materials and cleaning, Planned Parenthood's sex toy safety guidance and the research summary at PubMed on sex toy dimensions are both worth reading.