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A 40-inch chest is size M (101.6 cm). Enter your chest measurement in inches and this chart returns your men's t-shirt size, with the full table, the between-sizes rule, and what to do when you fall outside the chart.
Men's t-shirt sizes are chest bands, not single numbers: each size covers a two-inch range, and the right size is the band your chest measurement falls inside. Measure around the fullest part of your chest, level, over a thin shirt, and let the chart do the rest.
| Size | Chest (inches) | Chest (cm) |
|---|---|---|
| S | 34–36 | 86.4–91.4 |
| M | 38–40 | 96.5–101.6 |
| L | 42–44 | 106.7–111.8 |
| XL | 46–48 | 116.8–121.9 |
| XXL | 50–52 | 127.0–132.1 |
Print this table and keep it with your tape measure: inches on the left, centimetres on the right, converted at 1 inch = 2.54 cm. The bands are the standard men's pattern used by most brands; any single brand's chart can shift by an inch, so when a brand publishes its own numbers, those win over this general chart.
Stand relaxed, arms at your sides, and run the tape around the fullest part of your chest, level all the way around, over a thin t-shirt — not over a jacket, and not pulled tight. Breathe out normally and read the number; a tape pulled tight or held high under the arms will read small and push you into a size that binds. If your number falls inside a band, that band is your size: 36 inches is S, 40 is M, 44 is L, 48 is XL, and 52 is XXL. If it falls between bands — 37, 41, 45, or 49 inches — this chart sizes up: 37 goes to M, 41 to L, 45 to XL, 49 to XXL, because a slightly roomy shirt is wearable and a slightly tight one is not. The exception is a fitted cut in a stretchy fabric, where sizing down to the smaller band is reasonable if you prefer it close. Below 34 inches you are under this chart: re-measure first, since a low reading usually means the tape slipped, and then check youth sizes or small-cut brands. Above 52 inches you are over it: XXL is the top here, so look for extended, big, or tall ranges and check that brand's own chart, since extended sizing varies more than standard sizing does.
| Output | Formula | What it means |
|---|---|---|
| Chest in cm | Inches × 2.54 | 40 in = 101.6 cm at the default. |
| Size lookup | Band containing the chest measurement | 40 in falls in 38–40, so size M. |
| Between sizes | Next band up (37 → M, 41 → L, 45 → XL, 49 → XXL) | Size up for comfort; size down only for a fitted stretch cut. |
| Below the chart | Under 34 in | Outside this chart: re-measure, then check youth or small-cut sizes. |
| Above the chart | Over 52 in | Outside this chart: look for extended, big, or tall ranges. |
This is a general men's chart, not any single brand's chart: brands shift bands by an inch or so, cuts differ (classic, slim, relaxed), and fabrics shrink or stretch differently, so a brand's own published chart always wins when one exists. The lookup assumes an adult men's standard cut; it does not cover women's, youth, tall, or athletic cuts, and it uses chest only — shoulder width, length, and body shape also affect fit. Measure over a thin shirt, level, and relaxed: a tight or high tape reads small and will push you into a size that binds. When in doubt between two sizes, order both if returns are free.
Bright Side Kit. "T-Shirt Size Chart: Chest Measurement to Size Lookup" https://brightoolbox.com/t-shirt-size-chart/ Accessed October 24, 2026.Size M. The M band is 38–40 inches (96.5–101.6 cm), and 40 inches is 101.6 cm.
Size S. The S band is 34–36 inches (86.4–91.4 cm), and 36 inches is the top of that band.
Size L. The L band is 42–44 inches (106.7–111.8 cm), and 44 inches is the top of that band.
Size XL. The XL band is 46–48 inches (116.8–121.9 cm), and 48 inches is the top of that band.
Size up: 41 inches goes to L. The rule on this chart is 37 to M, 41 to L, 45 to XL, and 49 to XXL. Size down only if you prefer a fitted cut and the fabric has stretch.
You are below this chart: the smallest size here is S (34–36 in). Re-measure over a t-shirt first, since a low reading usually means the tape slipped, then check youth sizes or a brand that cuts small.
You are above this chart: the largest size here is XXL (50–52 in, 127.0–132.1 cm). Look for extended, big, or tall ranges, and check that brand's own chart, since extended sizing varies the most.
Stand relaxed with arms at your sides, run the tape around the fullest part of your chest, level all the way around, over a thin t-shirt. Breathe out normally and read the number; do not pull the tape tight or hold it high under the arms.