How to Choose the Right Silicone Cock Ring Size: 40mm vs 45mm vs 50mm

Quick answer

Choose the largest silicone cock ring that stays in place without pinching or discoloration. Measure the circumference of your erect penis at the base, divide by 3.14 to get diameter, then round down to the nearest 5mm. A 40mm ring fits most penises 125–135mm around; 45mm fits 135–150mm; 50mm fits 150–165mm. If you are between sizes, start with the larger ring and size down only if it slips.

Measure at the base, not the middle

Wrap a flexible tape measure or a strip of paper around the base of your erect penis, where the ring will sit. Pull it snug but not tight. Write down the circumference in millimeters. Do this three times on different days to account for natural variation. The average of those numbers is your working measurement.

Convert circumference to diameter

Divide your average circumference by 3.14 (pi) to get the diameter. For example, 140mm circumference ÷ 3.14 = 44.6mm diameter. Cock rings are sold by inner diameter, so round down to the nearest standard size: 40mm, 45mm, or 50mm. Rounding down ensures a snug hold; rounding up may cause slipping.

Match diameter to the 40mm / 45mm / 50mm range

Use this cock ring sizing chart as a starting point:

40mm inner diameter: best for 125–135mm circumference (about 1.6–1.7 inches diameter).

45mm inner diameter: best for 135–150mm circumference (about 1.7–1.9 inches diameter).

50mm inner diameter: best for 150–165mm circumference (about 1.9–2.1 inches diameter).

If your measurement falls between two sizes, choose the larger size first. A ring that is too small can restrict blood flow and cause numbness.

Test fit with a multi-size pack

A three-size pack lets you try 40mm, 45mm, and 50mm under real conditions without guessing. Start with the largest ring. Apply a water-based lubricant to the base of the penis and inside the ring. Slide it on. It should feel snug but not painful. You should be able to fit one fingertip under the ring. If you cannot, it is too tight. If it slides off easily when erect, it is too loose. Wear each size for no more than 20 minutes the first time. Check for redness, numbness, or a cold feeling. Remove immediately if any occur.

Material matters for sizing accuracy

Solid silicone stretches less than TPE or rubber, so its sizing is more predictable. A 100% solid silicone ring will not stretch as much over time, meaning the diameter you choose is the diameter you get. This makes silicone a good choice for a first cock ring because you can rely on the labeled size. However, less stretch also means you have less margin for error—so measure carefully and size up if unsure.

Step-by-step fit check

1. Measure erect circumference at the base: Use a flexible tape or paper strip. Record in millimeters. Repeat three times and average. Common mistake: measuring flaccid. Always measure erect for a cock ring.
2. Calculate diameter and round down: Divide circumference by 3.14. Round down to the nearest 5mm (40, 45, or 50). Checkpoint: if you are between sizes, choose the larger one first.
3. Try the largest size first: Lubricate, slide on, and check that one fingertip fits under the ring. Wear for 20 minutes max initially. Stop immediately if you feel numbness, pain, or discoloration.
4. Adjust based on hold and comfort: If the ring slips off when erect, size down. If it pinches or leaves marks, size up. Never wear a ring that restricts blood flow for more than 30 minutes.

Product facts

• Silicone Cock Ring Pack, 40mm / 45mm / 50mm: REGULATION Branded Silicone 3 Cock Ring Pack includes inner diameters of 40mm, 45mm, and 50mm, with outer diameters of 50mm, 55mm, and 60mm, all 5mm thick, and 100% solid silicone. Having all three sizes in one pack lets you compare fit directly and find your correct diameter without buying multiple single rings.