Measure erect. Pick the ring you're sizing for, enter what you measured, and the calculator tells you which size (and shape) to order. How to measure each ring is below the calculator.
The 2mm rule
A rigid ring (The Pinnacle, The Clarifier, The One, the Fat Ring) fits best about 2mm under what you measure. It presses in a little, contacts well when you start soft, and holds when you're hard. The calculator already takes the 2mm off for you. The flexible TPU rings (the Proppers) are the opposite: their opening is bigger than you are, see below.
What to measure with
Best: the PlaStim Caliper (ME-CAL). Soft tissue reads whatever you squeeze it to, so the caliper has a built-in touch indicator: close it until the two lines meet and every reading is taken at the same light force (about 1 N). Put what you measure on the "place here" line across the jaws. The standard beam reads 0–56mm, which covers every ring on this page.
For the shaped rings: the PlaStim Fit Gauge (ME-FIT). Seven pins measure the real cross-section, not just two numbers. Choose "Fit Gauge" in the calculator and enter the seven readings.
No caliper? A cloth tape, or a shoelace or string and a ruler, still works for the round rings below. Pull it snug, not tight, and measure the same way each time.
The Pinnacle and The Clarifier
These are not round, so they are sized by two numbers instead of one. String can't give you these; the caliper or the Fit Gauge can.
- Width: side to side
- Depth: front to back
Example: the caliper reads 36mm side to side and 34mm front to back. Take off the 2mm and your ring size is 34 × 32mm. Enter 36 and 34 in the calculator above (or the fitting tool on the product page) and it picks the width and the shape. You can also send the two numbers in Discord or by email.
The Pinnacle: tip / under the corona
The Clarifier: bipolar shaft ring
The Propper Grow and The Propper Spikey (shaped TPU rings)
These are shaped, not round, and made of flexible conductive TPU. You pick two things: a Base (the shape) and a Size (the opening). Measure the width and depth at the base of the shaft, erect.
- Base: divide depth by width and pick the closest. Base 1 = 0.89, Base 2 = 0.98, Base 3 = 1.013.
- Size: order the opening 4–5mm LARGER than your erect width. No 2mm rule here: the soft TPU fingers or spikes press in as you grow. Your width should land inside the opening's "usable" range shown on the product page.
Example: 38mm wide and 37mm deep. 37 ÷ 38 = 0.97, closest to Base 2 (0.98). The opening is 38 + 4–5 = 42–43mm, so order the 42.5mm opening (usable 29.5–39.5mm, and 38 is inside it).
The Grow and the Spikey are sized the same way.
The Propper Grow
The Propper Spikey
Round rings (The One, Fat Ring, Underball)
These rings are sized by diameter.
The One (shaft ring): measure at the base of the shaft, right up against your body. Nothing goes under the testes.
- With the caliper: measure the width and the depth there and enter them in the calculator above. By hand: average them, then take off 2mm. Example: 38mm wide and 36mm deep: (38 + 36) ÷ 2 = 37mm, so a 35mm ring. (The calculator works the diameter out from the shape, so it can land 1mm higher.)
- With string: wrap it around the base, snug but not tight, divide the length by 3.14, then take off 2mm. Example: 116mm of string ÷ 3.14 = 37mm, so a 35mm ring. The conversion list is at the bottom of this page.
This ring changes size the most from flaccid to erect. Sized 2mm under, it contacts well when starting flaccid and acts as a cock ring when erect. Usually 33–43mm.
The Fat Ring: a round shaft ring, so measure it exactly like The One, same place, same method, same 2mm off. Sizes run 25–65mm: 1mm steps up to 46mm, then 2mm steps. Between two sizes, pick the smaller one.
The One Underball: this one wraps the base of the penis AND under the testes (the whole package), so it is measured with string. Pull it snug but comfortable. Example: 157mm of string ÷ 3.14 = 50mm. Flaccid to erect does not change this one as much: measure erect, put it on flaccid. Usually 45–55mm.
Circumference to Diameter Conversion
- 94mm (3.70") → 30mm diameter
- 97mm (3.82") → 31mm diameter
- 101mm (3.98") → 32mm diameter
- 104mm (4.09") → 33mm diameter
- 107mm (4.21") → 34mm diameter
- 110mm (4.33") → 35mm diameter
- 113mm (4.45") → 36mm diameter
- 116mm (4.57") → 37mm diameter
- 119mm (4.69") → 38mm diameter
- 123mm (4.84") → 39mm diameter
- 126mm (4.96") → 40mm diameter
- 129mm (5.08") → 41mm diameter
- 132mm (5.20") → 42mm diameter
- 135mm (5.31") → 43mm diameter
- 138mm (5.43") → 44mm diameter
- 141mm (5.55") → 45mm diameter
- 145mm (5.71") → 46mm diameter
- 148mm (5.83") → 47mm diameter
- 151mm (5.94") → 48mm diameter
- 154mm (6.06") → 49mm diameter
- 157mm (6.18") → 50mm diameter
- 160mm (6.30") → 51mm diameter
- 163mm (6.42") → 52mm diameter
- 166mm (6.54") → 53mm diameter
- 170mm (6.69") → 54mm diameter
- 173mm (6.81") → 55mm diameter
- 176mm (6.93") → 56mm diameter
- 179mm (7.05") → 57mm diameter
- 182mm (7.17") → 58mm diameter
- 185mm (7.28") → 59mm diameter
- 188mm (7.40") → 60mm diameter
- 192mm (7.56") → 61mm diameter
- 195mm (7.68") → 62mm diameter
- 198mm (7.80") → 63mm diameter
- 201mm (7.91") → 64mm diameter
- 204mm (8.03") → 65mm diameter