Girth to Diameter
Type the distance around anything round, its girth, and see how wide it is across. Works the other way too, in inches, cm or mm.
Going from girth to diameter means turning the distance around something round into the distance straight across it. For a circle, the distance around is about 3.14 times the distance across its center. That number, about 3.14, is called pi, and the converter does the dividing for you. A 5-inch girth, for example, is about 1.59 inches across.
Girth to diameter chart
The chart also shows the radius, which is the distance from the center to the edge, and the flat width, which is half the girth of a round tube laid flat. Picture an empty bicycle inner tube pressed flat on a table: the flat width is how wide it lies.
The first table is in inches and the second in centimeters (cm). Ten millimeters (mm) make one centimeter.
Find your girth in the first column, then read across the row for the other measurements.
In inches
| Girth (in) | Diameter (in) | Radius (in) | Flat width (in) |
|---|---|---|---|
| 3 | 0.95 | 0.48 | 1.50 |
| 3.5 | 1.11 | 0.56 | 1.75 |
| 4 | 1.27 | 0.64 | 2.00 |
| 4.5 | 1.43 | 0.72 | 2.25 |
| 5 | 1.59 | 0.80 | 2.50 |
| 5.5 | 1.75 | 0.88 | 2.75 |
| 6 | 1.91 | 0.95 | 3.00 |
| 6.5 | 2.07 | 1.03 | 3.25 |
| 7 | 2.23 | 1.11 | 3.50 |
| 7.5 | 2.39 | 1.19 | 3.75 |
In centimeters
| Girth (cm) | Diameter (cm) | Radius (cm) | Flat width (cm) |
|---|---|---|---|
| 9 | 2.86 | 1.43 | 4.5 |
| 10 | 3.18 | 1.59 | 5.0 |
| 11 | 3.50 | 1.75 | 5.5 |
| 12 | 3.82 | 1.91 | 6.0 |
| 13 | 4.14 | 2.07 | 6.5 |
| 14 | 4.46 | 2.23 | 7.0 |
| 15 | 4.77 | 2.39 | 7.5 |
| 16 | 5.09 | 2.55 | 8.0 |
| 17 | 5.41 | 2.71 | 8.5 |
| 18 | 5.73 | 2.86 | 9.0 |
Going from diameter to circumference
If you know the width across instead, pick Diameter in the converter and it shows the distance around. Here are a few common sizes:
| Width across | Circumference |
|---|---|
| 1 in | 3.14 in |
| 1.5 in | 4.71 in |
| 2 in | 6.28 in |
| 2.5 in | 7.85 in |
| 3 in | 9.42 in |
| 4 in | 12.57 in |
How to measure girth
A soft, bendable tape is the easiest choice, since it hugs the curve, and an inexpensive sewing tape is perfectly fine.
- Wrap the tape once around the object at the right spot for that object, which is not always the widest point.
- Let it rest flat on the surface without pressing in, or the number will read too small.
- Check the number where the tape's end crosses the rest of it.
No tape handy? Wrap a piece of string around, mark the spot where it meets itself, then stretch it out next to a ruler.
Where to measure girth
People measure girth for all sorts of reasons, from trees and rings to bodies and parcels. The correct place changes with the thing you're measuring:
- Tree: in the US, the usual height is 4.5 feet off the ground, per Portland's tree guide. In many other countries, people measure at 1.3 meters.
- Pipe: around its outer wall.
- Wrist: right above the wrist bone, where a watch would rest, tape lying flat on skin without pulling it snug.
- Finger: around the finger's base. When your knuckle is bigger, measure both spots and pick a ring size between them.
- Penis: one loop around the shaft's widest point.
- Belly: around the middle, typically at the navel (belly button).
- Parcel: wrap the tape around its thickest part, across the parcel and not from end to end.
Girth meaning
Merriam-Webster describes girth as a measurement around a body, like the girth of a tree. With a round shape, girth means the same as circumference.
In health care, girths are tape measurements made at set points on the body. In shipping, girth means the distance around the widest part of a parcel.
Girth vs diameter
Girth measures the way around an object. Diameter measures straight through the middle, from one side to the other. For anything circular, the girth comes out to roughly 3.14 times the diameter.
Converting girth to diameter is only perfectly accurate for a true circle. Tree trunks aren't perfectly round, so for a tree the answer is a close estimate rather than an exact width.
Average girth
In short: when it is hard (erect), an average penis measures about 11.66 cm around, which is 4.59 inches. When it is soft (flaccid), the average is about 9.31 cm around. Health professionals took these measurements; the men did not measure themselves.
How we know these averages
The biggest review of measured research combined 17 studies covering as many as 15,521 men, every one measured by a health professional. The review's average erect girth was 11.66 cm, based on 381 men, which is about 4.59 inches around and 3.71 cm across. Average flaccid girth came to 9.31 cm. The measurements were taken at the base or mid-shaft, which means halfway along.
A more recent review of 5,168 men put average erect girth at 11.91 cm. It also found that average flaccid girth changes from one world region to another:
| World region | Typical flaccid girth |
|---|---|
| Americas | 9.74 cm |
| Europe | 9.36 cm |
| South-East Asia | 9.14 cm |
| Eastern Mediterranean | 8.96 cm |
| Africa | 8.78 cm |
| Western Pacific | 8.40 cm |
The math behind these numbers
Divide the girth by pi, roughly 3.1416, to find the diameter. Multiply the diameter by pi to find the girth. The radius is half of the diameter, and the flat width is half of the girth. There are exactly 2.54 centimeters in an inch.
To change a girth into a diameter, take the distance around and divide it by pi, and you get the width measured straight across. Take a 5-inch girth: dividing by pi gives a width of about 1.59 inches from one side to the other.
Doubling the nominal width gives the condom's circumference, which should be a little smaller than your girth to help the condom stay in place.
Questions people often ask
How can I check that my string method is working?
Try it on a toilet paper tube. A standard tube is about 5 inches around and 1.6 inches across, so your string should measure close to 5 inches.
How does girth relate to condom sizing?
Condom sizing uses nominal width, which is how wide the condom is when pressed flat, measured at or near the opening. A condom should be a little smaller around than you are, so that it stays on. The usual width groups look like this:
| Your girth | Condom size | Width when flat |
|---|---|---|
| 100 to 110 mm | Snug | under 52 mm |
| 110 to 120 mm | Regular | 52 to 54 mm |
| 120 to 135 mm | Large | 55 to 60 mm |
| 135 to 165 mm | Extra large | 64 to 72 mm |
What does girth mean when shipping a package?
On a round parcel, the girth is simply its circumference. According to the US Postal Service, most commercial parcels can't exceed 108 inches when length and girth are added together.
Why is a pipe's diameter different from its size name?
The actual outside diameter of a pipe is bigger than the number in its name. A pipe that measures 5.97 inches around comes out to 1.900 inches wide, and it's sold under the name 1 1/2 inch pipe, even though it is almost 2 inches across.