Car Seat Guide Calculator
Find the right car seat type for your child based on their age, weight, and height.
Covers rear-facing, forward-facing, and booster seats.
Car seat sizing matches a child’s weight, height, and age to the correct car seat category and installation method. Using the wrong seat — or improperly installing the right one — is the leading cause of child injury in vehicle crashes.
Seat Categories by Size:
| Seat Type | Child Weight | Child Height | Age |
|---|---|---|---|
| Infant (rear-facing only) | Up to 13 kg (30 lbs) | Up to 83 cm (32.5 in) | Birth–12 months |
| Convertible (rear-facing) | Up to 18–23 kg | Up to 110 cm (43 in) | 0–2+ years |
| Convertible (forward-facing) | 9–29 kg (20–65 lbs) | Up to 127 cm (50 in) | 2–7 years |
| Booster seat | 18–36 kg (40–80 lbs) | 95–145 cm | 4–12 years |
| Seat belt only (vehicle belt) | 36+ kg and 145+ cm | Over 145 cm | 8–12+ years |
Weight and Height Check Formula:
Child is ready to advance when EITHER:
- Weight exceeds the seat’s rated maximum, OR
- Head is within 2.5 cm (1 inch) of the top of the seat shell
Worked Example:
Child: 3 years old, 16 kg, 95 cm tall.
- Not yet at convertible rear-facing weight limit (18–23 kg)
- Head below top of shell
- Keep rear-facing — this is the safest position even at age 3
At 18 kg or when head reaches limit: switch to forward-facing with 5-point harness.
LATCH Weight Limit:
The LATCH system (Lower Anchors and Tethers for Children) is rated to child + seat weight of 29 kg (65 lbs). Above this, use the seatbelt to install even if LATCH hardware is present.
Practical Tips:
- Rear-facing is always safer until the child outgrows the rear-facing weight/height limit
- Harness straps should be snug: you should not be able to pinch the webbing at the shoulder
- Get a certified car seat technician to check your installation — errors are extremely common
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.