What is i-Size?
Short answer: i-Size refers to the R129 car seat regulation. The Lullaby Trust lists R129, or R44.04 and R44.03, with the 'E' mark, as the standards to look for.
Here is the detail behind that answer, taken from current UK guidance from the NHS and the Lullaby Trust.
Things to check
- Look for R129 (i-Size) or R44.04 approval and the E mark.
- Check the fit in your car and whether you need an ISOFIX base.
- Take your baby out when you arrive, as the NHS advises.
What the guidance says
- Car seats: look for ECE R44.04 (or R44.03) or i-Size R129, shown by the 'E' mark label.
Related questions
What is a infant car seat?
A rear-facing car seat for newborns, often clicking onto a pushchair.
Shop at Baby Kingdom
- Radial i-Size Plus 360 Spin 40-150cm Car Seat
- Cirrus i-Size Car Seat
- Nimbus 180° Spin i-Size Car Seat
- Venus Prime Jogger Stroller & Rotating Group 0+/1/2 ISOFIX Car Seat
Check each product page for its exact dimensions, mattress size, age and weight limits and safety standards.
More advice
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Sources
- The Lullaby Trust: Baby mattresses and bedding (accessed 2026-10-21)
General information only, not medical advice. Always follow your product's instructions. If you are worried about your baby, contact your GP, health visitor or 111. In an emergency, call 999.