Car seat fit calculator
Save one vehicle and one child-restraint measurement set. The output is a screening report plus a printable checklist.
Width: use the narrowest real constraint
For one seat, compare the restraint’s widest point with the usable part of the vehicle cushion and door/armrest geometry. For two or three seats, the widest point of each shell is not enough: adjacent seats may puzzle together at different heights. A narrow base with wide shoulder wings can fit next to a seat whose widest part sits lower, while two nominally “17-inch” seats can still interfere.
Cushion depth and overhang
Some child restraints permit a portion of the base to extend beyond the front edge of the vehicle cushion; others impose a specific maximum overhang or require a certain percentage of the base to be supported. Never invent a percentage. Enter the base footprint here to spot a possible mismatch, then check the restraint manual for the actual rule.
Front-to-back room
Rear-facing seats consume space differently depending on recline angle and the child’s stage. Some allow a more upright angle for an older child; newborn use often requires more recline. Vehicle and child-restraint manuals also differ on whether the restraint may touch the front seat. Measure with the front seat adjusted for the person who actually drives or rides there.
Physical test-fit checklist
Related guides & tools
Sources & verification
Use this page as a planning aid, not a replacement for the manuals. Child restraints and vehicles have model-specific requirements. Verify your child restraint manual, vehicle owner's manual and current manufacturer guidance before installation.
- NHTSA — Car Seats & Booster Seats
- NHTSA — Car Seat Finder
- NHTSA — Air Bags
- American Academy of Pediatrics — Car Seats: Information for Families
- American Academy of Pediatrics — Rear-Facing Car Seats for Infants & Toddlers
- American Academy of Pediatrics — 2026 Car Seat Product Listing
Safety guidance reviewed September 23, 2026.