PTP measurement stands for “pit to pit,” a method of measuring the width of a garment by laying it flat and measuring across the chest from one armpit seam to the other. It’s the most reliable way to determine how a shirt, jacket, or sweater will actually fit you, and it’s widely used in online clothing listings, vintage shops, and brand size guides. You may also see PTP refer to Precision Time Protocol in networking or point-to-point distance in surveying tools, but in everyday searches, pit to pit is by far the most common meaning.
How Pit-to-Pit Measurement Works
To measure pit to pit, lay the garment face-up on a flat surface and smooth out any wrinkles. Place one end of a fabric tape measure about one inch below the armpit seam on one side, then stretch it straight across to the same point on the opposite side. The measurement starts and ends at the fabric itself, not at the seam stitching. This gives you the garment’s half-chest width in inches or centimeters.
You’ll typically see PTP listed on resale sites, thrift stores, and brand websites because it removes the guesswork of inconsistent sizing labels. A “medium” from one brand might measure 20 inches pit to pit while another brand’s medium measures 22 inches. The raw number tells you exactly how wide the garment is, regardless of what the tag says.
Pit to Pit Is Not the Same as Chest Size
A common mistake is treating your PTP measurement as half your chest circumference. They’re related but not identical. Your chest measurement is taken around the fullest part of your torso with a tape measure wrapped all the way around your body. Pit to pit measures only the front panel of the garment laid flat, which doesn’t account for the curve of your back, the thickness of the fabric, or how much ease (extra room) the garment is designed to have.
If you know your chest circumference, you can use it as a rough reference. Divide it by two to get a starting point, then add one to two inches for a relaxed fit. But the most accurate approach is to measure a garment you already own that fits the way you like, then compare that PTP number to the one listed in a size chart or product listing.
When PTP Matters Most
Pit-to-pit measurement is especially useful when you’re buying clothes online and can’t try them on. Sellers on secondhand platforms routinely include PTP in their listings because it gives buyers a concrete number to compare against their own wardrobe. It’s also the standard in vintage clothing, where original size labels often don’t correspond to modern sizing at all. A vintage large from the 1970s may fit closer to a modern small.
Brand size guides sometimes list PTP alongside other measurements like body length (from the highest point of the shoulder to the hem) and sleeve length. Together, these three numbers give you a reliable picture of fit without stepping into a dressing room.
Tips for an Accurate Measurement
- Use a flat, hard surface. A bed or couch can cause the fabric to bunch. A table or hardwood floor works best.
- Button or zip the garment closed. This keeps the front panel aligned the way it would sit on your body.
- Measure the same spot consistently. About one inch below the armpit seam is the standard reference point. Going higher or lower by even half an inch can shift the number.
- Use a fabric tape measure. A rigid metal tape measure won’t conform to the garment and can give slightly inflated readings.
- Measure more than one garment. Comparing PTP across a few shirts you already own helps you identify the range where you’re most comfortable.
PTP in Other Contexts
Outside of clothing, PTP can refer to Precision Time Protocol, a network synchronization standard defined by IEEE 1588. It allows devices on a network to synchronize their clocks to sub-microsecond accuracy, with newer versions supporting precision better than one nanosecond. PTP achieves this through hardware timestamping and specialized network equipment called boundary clocks and transparent clocks. It’s used in telecommunications, power utilities, and financial trading systems where even tiny timing discrepancies matter. By comparison, the more common Network Time Protocol (NTP) that syncs your computer’s clock is only accurate to a few milliseconds, which is fine for everyday use but far too imprecise for industrial applications.
PTP can also stand for point-to-point measurement in laser distance tools. Devices from companies like Leica Geosystems let you measure the distance between two remote points from a single location. You target each point separately, and the tool calculates the straight-line distance, height difference, horizontal distance, and angle between them. This is useful in construction and architecture when the two points are physically inaccessible.
For most people searching “PTP measurement,” though, the answer is simpler: grab a tape measure, lay your shirt flat, and measure from pit to pit.