Most carriers come with both lower and upper weight limits. In the sling library, we work for more often with the constraints of the lower limits, carriers suitable from 5lb, or 15lb, for example, work in very different ways. It is very important that a carrier is appropriate for the size of a child as well as offering growing room. But on our recent theme of toddler carriers, and even preschool sizes, the upper weight limits are what come into play.
How important are upper weight limits?
Observing the manufacturer’s upper weight limit is very important. Checking your carrier regularly for wear and tear if your child is approaching the weight limit is also a good idea. Ergonomic carriers are usually safety tested to a fairly high weight, and it is most common for a child to not need carrying any more before the weight limits comes into play. Nonetheless, it is a good idea to know the limit on the carrier you are using. Some carriers such as most brands of woven wrap have no practicable upper weight limit – as long as they are in good condition, the carrying strength of the adult is the only real limit. 
It is important to know that an upper weight limit does not mean a carrier is certified comfortable or safe up to that level. It is quite possible for a child to outgrow a carrier developmentally or in height well before they hit the upper weight limit.
What are the most common upper weight limits?
Different types of carrier tend to have different average limits. Front pack style carriers, with arm and leg holes, and a harness for the carrying adult, tend to have the lowest limits, as their way of distributing weight is not as effective as a more 
ergonomic option. Woven wraps and soft structured carriers tend to have the highest weight limits, with the toddler and preschooler size soft structured carriers having some of the highest. Upper weight limits are most often presented in pounds but we have referenced them in kilograms also.
So how long will my carrier last?
If you have a child who still wants to be carried, and you are happy to carry them, there are three main things to look for in how your carrier fits. Is the body height high enough, or can it become high enough via a headrest or adjustment, to support the child adequately? Your carrier should fit to firmly under the armpits as a minimum. Is the body width wide enough to support the legs, or can it be made wider using footrests like with the Boba 4G, or extenders such as the Tula Free to Grow width extensions? Ideally your child’s should be supported in a capital M shape. And what is the upper weight limit on your carrier? Is your child inside this limit?
As you can see in the following table, although all children are very different, in most cases upper weight limit is very generous and should last years, as well as inspire confidence in the structure and components of the carrier. Average weights taken from UK growth charts.
Be safe, be snug, sometimes bigger kids need a carry too!
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