Bike Inner Tubes: Sizing & Buying Guide

Inner tubes are sized by wheel diameter and a tire-width window, not by an exact match. Read the sidewall of your current tire - you'll see something like "700×25-32c" or "26×1.95" along with an ETRTO code (e.g. 25-622). The first number is wheel diameter, the second is tire width. Pick a tube whose width range covers your tire width: a 700×25-32c tube fits any 25-32 mm road tire, a 26×1.75-2.125 tube fits most 26" cruiser and MTB tires. Kids bikes use 12", 14", 16", 18", 20", and 24" wheels; most adult bikes are 26", 27.5" (650b), 29" (same ETRTO 622 as 700c), or 700c road. Match the valve type to your rim hole: Schrader (the wide "car" valve) for most kids, hybrid, and entry MTB; Presta (the slim threaded valve) for road, gravel, and higher-end MTB; Dunlop / Woods on some European city bikes.

• Valve type - Schrader fits any pump and any rim hole; Presta needs a Presta-compatible pump head and a narrower (6.5 mm) rim hole. If a Schrader-drilled rim is all you have, fit a $1 Presta grommet first so the slim valve doesn't slop in the oversized hole; never drill out a Presta rim to fit Schrader.
• Valve length - deep-section road and gravel rims (40 mm+) need 60 mm or 80 mm Presta valves. A 32 mm valve will sit below the rim surface and be impossible to inflate.
• Tube material - standard butyl is cheap, durable, and what 95% of riders should buy. Latex tubes shave ~30 g per wheel and roll faster, but lose pressure overnight and tear easily. TPU (thermoplastic polyurethane) tubes from Tubolito, Schwalbe Aerothan, and Pirelli weigh 30-40 g and pack to a deck-of-cards size - great as a spare even if you ride butyl daily.
• Self-sealing tubes - pre-loaded with sealant (Slime, Schwalbe SV) to plug small thorn punctures automatically. Heavier than standard tubes but a useful upgrade for goathead-thorn country, kids bikes that get neglected, and commuters.
• Kids-bike compatibility - cheap kids bikes from big-box stores often use Schrader valves and oddball tire widths (12½×2¼, 16×1.75). Look for multi-pack listings that explicitly list kids sizes, or buy a tube whose width range generously covers the printed tire size.
• Multi-pack value - buying 2-packs or 5-packs cuts per-tube cost roughly in half and means you have a backup the day you flat. Worth it for any rider doing more than a few miles a week.