ONYX General Purpose Boating Life Jacket Child, Red 30-50 lb $23.00 View on Amazon
Calculator
Life jacket (PFD) size calculator
Quick answerChildren's life jackets are sized by weight: infant under 30 lb, child 30 to 50 lb, youth 50 to 90 lb. Adults size by chest: universal adult vests fit roughly 30 to 52 inches, and larger chests need an oversize or plus-size vest.
Adult sizeL/XL (40 to 52 in)
Universal adult vestFits (30 to 52 in)
Inflatable belt pack or vestAllowed (adult, swimmer)
Weight checkOver 90 lb: adult class
Paddling vests have large arm openings and a short back so they do not fight a kayak seat. Try it sitting down.
Gear that fits your answer
Cards re-sort as you change the inputs: the ones that meet your numbers move to the front. Check each listing's rated capacity and dimensions before buying.
ONYX General Purpose Boating Life Jacket Child, Red 30-50 lb 
Stearns Kids Life Vest, USCG Approved, Type III, for Kids 30 to 50 Pounds USCG approved / 30-50 lb $38.02 View on Amazon
Airhead Infant Type II Life Jacket | US Coast Guard Approved | Closed Sided, Quick-Dry | Secure Buckles & Zipper | Wicked Kwik-Dry NeoLite Flex | Hot Pink USCG approved / 30-50 lb $47.62 View on Amazon
Body Glove Method Unisex Dual Size USGA Type III Life Jacket PFD- 2X/3X-Yellow USCG approved $64.99 View on Amazon
Sizing specs: Body Glove Method Unisex Dual Size USGA... 
BLUESTORM Cirrus26 Inflatable PFD Life Jackets for Adults | US Coast Guard Approved Automatic Life Vest w/Manual Override Convertibility (Legendary Tan) USCG approved $104.98 View on Amazon
Sizing specs: BLUESTORM Cirrus26 Inflatable PFD Life... 
Stohlquist Adult Life Jacket PFD 4-Pack. US Coast Guard Approved Type III Life Vest for Kayak, Boat, Paddleboard & Water Sports, Lightweight Adjustable Fit for Men & Women 90+ lbs USCG approved $169.99 View on Amazon
Sizing specs: Stohlquist Adult Life Jacket PFD... How the math works
weight under 90 lb -> USCG weight class | 90 lb and up -> chest circumference band -> size
Fit test: fasten everything, then have someone lift the jacket at the shoulders. If it rides up past the chin or ears, it is too big. Inflatable PFDs are only for adults 16 and older who can swim.
Life jackets are sized one of two ways. Children's jackets carry U.S. Coast Guard weight classes, because the buoyancy has to match the body. Adult jackets are sold by chest circumference. The calculator uses weight below 90 lb and chest above it, then tells you whether an inflatable PFD is an option: inflatable approvals only cover people 16 and older, and they are a poor choice for weak swimmers.
After sizing, always do the fit test: fasten every buckle and zip, tighten the side straps, and have someone lift the jacket at the shoulders. If it slides up past the chin or ears, it is too big.
Worked examples
| Scenario | Result | Size by | Crotch strap |
|---|---|---|---|
| 25 lb toddler | Infant (under 30 lb) | Weight | Required, keeps it from riding up |
| 42 lb child | Child (30 to 50 lb) | Weight | Required, keeps it from riding up |
| 75 lb child | Youth (50 to 90 lb) | Weight | Recommended |
| Adult, 38" chest | S/M (30 to 40 in) | Fits (30 to 52 in) | Allowed (adult, swimmer) |
| Adult, 46" chest | L/XL (40 to 52 in) | Fits (30 to 52 in) | Allowed (adult, swimmer) |
| Adult, 56" chest | 2XL/3XL (52 to 60 in) | No: buy by size | Allowed (adult, swimmer) |
Frequently asked questions
What size life jacket do I need?
Kids by weight: infant under 30 lb, child 30 to 50 lb, youth 50 to 90 lb. Adults by chest: roughly S/M 30 to 40 inches, L/XL 40 to 52 inches, 2XL/3XL 52 to 60 inches. Universal adult vests cover about 30 to 52 inches of chest.
Should a child life jacket be tight?
Snug, not constricting. The child should be able to breathe and move their arms freely, but the jacket must not ride up when lifted at the shoulders. Crotch straps on infant and child jackets stop the jacket slipping over the head in the water.
Is an adult universal life jacket one size fits all?
Universal adult vests fit most adults over 90 lb with chests from about 30 to 52 inches. Above 52 inches they will not close properly, so buy an oversize or plus-size vest sold by chest range.
On the water: Wear a properly fitted, USCG-approved life jacket every time, dress for the water temperature rather than the air, and check your state and local paddling regulations before you launch.
This is researched general information, not professional advice. Sizing figures are starting points: confirm against the maker's own sizing chart and the capacity printed on the boat or board.