You will need a way to measure: something like a cloth tape, or shoelace, string, etc.
Measurements should be made while erect.
IMPORTANT: Rings are sized by diameter, but you'll be measuring circumference with string.
To convert your measurement: Circumference ÷ 3.14 = Diameter (ring size)
A full conversion list is at the bottom of this guide.
R1 – "Base-of-shaft" ring (the cock-ring part, balls stay below it)
Wrap the string ONLY around the base of the shaft, right up against your body. The string does NOT go under the balls. Pull it snug but not tight. Mark this measurement → This is your R1 / Shaft-base ring size.
This ring is tricky to get right, as it's the one that changes sizes the most when going from flaccid to erect. I use one 1-3mm smaller than my measured size for two reasons: (1) when starting flaccid, the smaller size makes better contact, and (2) when erect, it acts as a cock ring.
Since rings are circular but the penis isn't perfectly round, rings will fit slightly tighter than your string measurement suggests.
Usually 33-43mm diameter(104-135mm circumference)
R2 – "Under-the-balls" ring (the big one that goes around shaft + balls)
Wrap the string around the very base of your penis AND under your balls (the whole package). Pull it snug but comfortable. Mark this measurement → This is your R2 / Penis-and-Ball ring size.
This ring is easier to size. The difference between flaccid and erect doesn't affect this ring as much. Measure while erect, but install while flaccid as it can be difficult to put on when erect.
Usually 45-55mm diameter(141-173mm circumference)
The Pinnacle (R3) – "Under-the-head" ring (coronal ridge / glans ring)
Wrap the string in the groove right below the head. Snug but not tight. Mark this measurement → This is your Pinnacle / head ring size. Exact size and slightly undersize work fine, the head is more squishy. If you are ordering the Corona Lock option, measure for exact size—the opening with this ring is smaller than the ring size for a perfect fit.
Usually 31-41mm diameter(97-129mm circumference)
Circumference to Diameter Conversion
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94mm (3.70") → 30mm diameter
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97mm (3.82") → 31mm diameter
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101mm (3.98") → 32mm diameter
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104mm (4.09") → 33mm diameter
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107mm (4.21") → 34mm diameter
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110mm (4.33") → 35mm diameter
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113mm (4.45") → 36mm diameter
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116mm (4.57") → 37mm diameter
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119mm (4.69") → 38mm diameter
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123mm (4.84") → 39mm diameter
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126mm (4.96") → 40mm diameter
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129mm (5.08") → 41mm diameter
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132mm (5.20") → 42mm diameter
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135mm (5.31") → 43mm diameter
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138mm (5.43") → 44mm diameter
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141mm (5.55") → 45mm diameter
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145mm (5.71") → 46mm diameter
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148mm (5.83") → 47mm diameter
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151mm (5.94") → 48mm diameter
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154mm (6.06") → 49mm diameter
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157mm (6.18") → 50mm diameter
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160mm (6.30") → 51mm diameter
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163mm (6.42") → 52mm diameter
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166mm (6.54") → 53mm diameter
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170mm (6.69") → 54mm diameter
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173mm (6.81") → 55mm diameter
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176mm (6.93") → 56mm diameter
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179mm (7.05") → 57mm diameter
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182mm (7.17") → 58mm diameter
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185mm (7.28") → 59mm diameter
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188mm (7.40") → 60mm diameter
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192mm (7.56") → 61mm diameter
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195mm (7.68") → 62mm diameter
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198mm (7.80") → 63mm diameter
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201mm (7.91") → 64mm diameter
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204mm (8.03") → 65mm diameter