You've found the shirt. Now the product page wants a neck size, a sleeve length, and a fit name - slim, tailored, regular, classic - and there's no tailor's tape within reach. Every "how to measure for a shirt" guide online repeats the same neck-and-sleeve trick, hands you one brand's size chart, and stops there. None of them explain why a 16 neck with a 34 sleeve fits completely differently from a 16 neck with a 36 sleeve, or why "slim fit" at one brand is roomier than "regular fit" at another - the exact mismatch that sends dress shirts back for exchange more than almost any other menswear category.
This guide covers the measuring method that actually works at home, a complete neck-and-sleeve to letter-size conversion chart, why fit names like slim and tailored can't be trusted across brands, and - once you have numbers you trust - how to save and compare shirts from multiple stores and preview a specific cut on your own photo with AI try-on before you buy, using a cross-store wishlist like Spree.
Why Guessing Your Shirt Size Goes Wrong
There is no single "shirt size" the way there's a single foot length. A dress shirt's fit depends on at least three numbers - neck, sleeve, and chest/waist cut - and a casual shirt collapses all of that into one letter that hides just as much variance underneath it. A collar measured too tight, a sleeve measured with a straight arm instead of a bent one, or a "slim fit" trusted at face value from an unfamiliar brand can all be off by a size or more before the order even ships. That's exactly why dress shirts are one of the most frequently exchanged menswear categories - not because people measure carelessly, but because the measurement alone doesn't carry across brands the way shoppers assume it does.
01
Collar pulled too tight
A tape snugged hard against your throat under-measures your neck by half an inch or more - enough to make a comfortable size feel like it's choking you on arrival.
02
Sleeve measured with a straight arm
Measuring sleeve length with your arm fully extended instead of slightly bent shortens the reading - the fabric needs the extra length for your elbow to bend once the shirt is on.
03
Trusting the fit name, not the chest measurement
"Slim," "tailored," and "athletic" describe completely different amounts of room depending on the brand - the actual chest and waist inches are what travel between brands, not the label.
04
One collar number, two different shirts
A dress shirt's neck size and sleeve length are sold as a pair for a reason - the same "16" collar paired with a shorter or longer sleeve changes the whole garment's proportions.
The Collar-and-Sleeve Method: How to Measure at Home
You'll need a soft tape measure, or a strip of string and a ruler if that's all you have. The whole thing takes about five minutes, and measuring a shirt you already own is a useful cross-check at the end.
1
Measure your neck
Wrap the tape around the base of your neck, where a buttoned collar would naturally sit, keeping it level all the way around. Note the number, then add half an inch for breathing room - that's your neck size.
2
Run the two-finger test
With the tape still around your neck at that measurement, try sliding two fingers between the tape and your skin. If they fit comfortably, the number is right; if it's tight, size up half an inch.
3
Measure your sleeve
Bend your arm slightly at the elbow, hand on your hip. Starting at the center back of your neck, run the tape across your shoulder point, down the outside of your arm, to your wrist bone. That total is your sleeve length.
4
Measure your chest
Wrap the tape around the fullest part of your chest, under your arms and across your shoulder blades, keeping it horizontal. This is what separates slim, tailored, and regular fit at any given neck size.
5
Cross-check against a shirt you already own
If you have a dress shirt that fits well, lay it flat and measure the collar from button to buttonhole edge, and the sleeve from the shoulder seam to the cuff. It's often a more reliable number than measuring your body alone.
Shirt Size Conversion Chart: Neck & Sleeve to Letter Size
Dress shirts are sized by neck and sleeve together; casual and fitted shirts collapse both into a single letter. Match your measured neck to the closest row, then check sleeve length against the range before ordering.
| Neck (in) |
Neck (cm) |
Sleeve range (in) |
Typical Letter |
| 14 – 14.5 | 36 – 37 | 32 – 33 | XS / S |
| 15 | 38 | 32 – 33 | S |
| 15.5 | 39 | 33 – 34 | S / M |
| 16 | 41 | 34 – 35 | M |
| 16.5 | 42 | 34 – 35 | M / L |
| 17 | 43 | 35 – 36 | L |
| 17.5 | 44 | 35 – 36 | L / XL |
| 18 | 46 | 36 – 37 | XL |
| 19 | 48 | 36 – 37 | XXL |
Treat this chart the way you would a clothing size conversion chart: a reliable starting point, not a guarantee. Some brands run sleeve lengths half an inch shorter at the same neck size, and a shirt's fit name adds a whole additional layer on top of both numbers.
Slim, Tailored, and Regular Fit: Why the Same Collar Number Fits Differently
This is the part most sizing guides skip entirely. Your neck and sleeve numbers tell a retailer which shirt to hand you - they say almost nothing about how much room that shirt leaves through the chest, waist, and arms. "Slim fit" at one brand can measure roomier through the chest than "regular fit" at another, and "tailored" sometimes splits the difference, sometimes doesn't exist at all, and sometimes means something closer to slim. The only number that actually transfers cleanly between brands is your chest measurement in inches - the fit name on the label is marketing language layered on top of it, not a standardized size category.
That gap is exactly why a neck-and-sleeve measurement that's correct on paper still produces a shirt that feels too tight across the chest or balloons at the waist once it arrives - the collar fit the body, but the cut didn't, and no amount of remeasuring the neck would have caught it.
What to Do Once You Know Your Size
Neck, sleeve, and chest numbers tell you which box to check at checkout - they don't tell you which shirt, from which brand's cut, actually looks right on you. That's a different problem, and it's the one a cross-store wishlist with AI try-on is built for.
1
Save candidates from any store
Get Spree from the App Store, then paste the product URL or share it in from any of 1,000+ stores - the photo, price, and size chart come along automatically.
2
Compare fit names side by side
Put the slim, tailored, and regular-fit shirts you're deciding between into one cross-store wishlist instead of a dozen open tabs, and line up their actual chest measurements before you choose.
3
Preview it on yourself
Use AI Virtual Try-On on your own photo to see how a specific cut actually looks on your build before you commit - a product photo on a stock model tells you far less about your own proportions.
Shoppers who used virtual try-on before buying returned items 36% less often (McKinsey, 2025) — fewer obvious mismatches reaching checkout, on dress shirts just as much as any other garment.
If you're sizing more than just a shirt for an order, how to measure yourself for online shopping covers the rest of the body the same way this guide covers your collar and sleeve, and suit and blazer virtual try-on picks up where this leaves off for full tailored outfits.
Frequently Asked Questions
How can I find my shirt size at home without a tailor?
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Measure your neck where a collar would sit, add half an inch for breathing room, then measure sleeve length from the center back of your neck, across the shoulder, to your wrist bone with your arm slightly bent. Match both numbers to a shirt size chart - the neck measurement gives you the collar size and the sleeve measurement confirms it. If you own a dress shirt that already fits well, measuring it flat is often more reliable than measuring your body.
Is the tape-measure method for shirts actually accurate?
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It gets most people within half an inch on the collar, which is usually enough to land on the right size, but it isn't a tailor's fitting. A tape pulled too snug under-measures your neck, and bending your arm too much or too little when measuring sleeve length can shift the reading by close to an inch. Measure twice and use the two-finger test - you should be able to slide two fingers between your neck and the tape without it feeling loose.
Why do my collar and sleeve numbers not match a single letter size?
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Dress shirts are sized by two separate numbers - neck and sleeve - because the two don't scale together for every body. A 16 neck with a 34 sleeve and a 16 neck with a 36 sleeve are both labeled "size 16" on the collar but fit very differently through the arm. Casual shirts collapse both into one letter (S/M/L), which is why a casual-shirt Medium and a dress-shirt 15.5/33 can come from the same brand and still describe two different bodies.
Do shirt sizes differ between brands, and is slim vs. regular fit reliable?
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Yes, significantly, and fit-name labels make it worse, not better. One brand's "slim fit" sits closer to another brand's "regular fit," and "tailored," "athletic," and "classic" all mean different amounts of room through the chest and waist depending on who's using the label. Your neck and sleeve numbers stay constant across brands; the fit name on top of them does not, so always check the specific brand's own chest and waist measurements before ordering by fit name alone.
Does Spree help with shirt sizing?
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Not by measuring your neck or arms - Spree is upfront about that. Its job starts once you have your numbers: save shirts you're considering from any store into one wishlist, compare their size charts and fit names side by side, and use AI Virtual Try-On on your own photo to see how a specific cut actually looks on you before you order. It won't give you a collar size, but it's the best way to narrow down which shirt to size for in the first place.
The Bottom Line
Finding your shirt size at home is a solved problem - a tape measure, five minutes, and a correct bend in your elbow get you a neck and sleeve number close enough to order with real confidence. The quiet variable almost every guide skips is that those two numbers describe the collar, not the cut - and a "slim fit" or "tailored fit" label means something different at every brand that uses it.
Once you trust your numbers, the harder decision is usually which shirt, from which brand's specific cut, actually looks right on you - and that's where comparing real candidates from different stores side by side, and previewing each one on your own photo with AI try-on, saves far more regret than the measuring step ever did.