How to Measure Your Child

Accurate height and weight measurements are essential when choosing a safe, properly fitting car seat. While it is common to focus on age, car seats are designed around size, not birthdays. Measuring your child regularly helps you stay within the seat’s limits, avoid unexpected outgrowing, and choose the safest option for their next stage.

Below is a simple guide based on our How to Measure Your Child infographic, covering how to measure both height and weight for babies, toddlers and older children.

Measuring Height

Babies and Young Children

For little ones who cannot stand, measuring length on the floor is the most reliable method.

• Place your baby on the floor with their head resting flat against the wall or skirting board.

• Hold a book upright against the soles of their feet to create a firm, straight edge.

• Measure the distance from the wall to the book.

• Make sure their legs are straight and not curled up, as even a slight bend can affect the measurement.

This gives the clearest picture of your child’s true height while they are lying flat.

Older Children

Once children can stand confidently:

• Stand them straight with their heels, bottom and back against a wall.

• Place a book flat on the top of their head, ensuring it is level.

• Measure from the underside of the book to the floor.

This is the same method used by schools and health professionals for consistent accuracy.

Measuring Weight

Babies and Young Children

If you do not have baby scales, you can use the simple two-step method:

• Weigh yourself.

• Hold your baby and weigh again.

• Subtract your weight from the combined weight.

This gives a quick and reliable result. Baby scales can be purchased if you prefer, but they are not essential.

Older Children

Older children can stand on regular bathroom scales as normal. Ensure they are centred on the scale and standing still to avoid fluctuations.

If you do not have scales at home, most chemists, leisure centres or even friends and relatives will usually allow you to borrow theirs.

Why These Measurements Matter

Every car seat has clear height and weight limits that must be followed for safety. A seat that is too small or too large cannot protect a child properly in a crash. R129 seats are height and weight based. R44 seats are strictly weight grouped. Accurate measurements ensure your child remains in the correct category for their size, with the right fit and protection.

Checking measurements every few months (or more often during growth spurts) helps you stay ahead so you can plan for the next stage safely and confidently.

Using the Red Book and Centiles

Your child’s red book is a useful tool for planning ahead. Plotting their height and weight on the centile charts shows how steadily they follow their own natural growth curve. Once you know your child’s centile line, you can use it to estimate when they are likely to reach the height or weight limits of a seat. For example, a child on the 91st centile for height will usually reach the maximum height of a baby seat much earlier than a child on the 25th centile. Following their curve helps you predict when a seat will be outgrown and whether you may need a seat with higher limits, such as an extended rear facing option that goes to 125cm or 36kg.

FAQs

How often should I measure my child?

Every few months is usually enough, but during rapid growth phases it is worth checking more frequently. If your child is close to their seat’s limits, measure monthly to ensure they remain within the safe range.

Should I measure height and weight with or without shoes or clothes?

Always measure height without shoes so you get a true, consistent measurement. For weight, babies and toddlers are best weighed without clothes or in a clean nappy. Older children can be weighed in light clothing, but avoid bulky layers or heavy pockets as these will artificially increase their weight.

My child won’t stay still. How can I get an accurate measurement?

For babies and toddlers, try measuring when they are calm, fed and not overtired. A second adult can help gently keep legs straight or support them. For older children, turn it into a quick game or allow them to hold a toy. Taking two or three measurements and using the most consistent result can help with wriggly little ones.