# Order of a leaf node in B+ Tree

Going with the definition, that order of a B+ tree is the maximum number of children a node can have.

What is exactly meant by the order of a leaf node? As per my understanding order of a leaf node is the number of pairs it can hold.

But in general when order of a B+ tree is defined in a question like, order is 5. Example:https://www.tutorialcup.com/dbms/b-tree.htm . Then we assume the leaf nodes to have keys in [n/2] to n-1(3 to 4).

If we assume the leaf can contain 5 pairs, then the upper limit on keys should be 5 and not 4. Could someone explain why its taken to be n-1 in every B+ tree insertion tutorial.

• Why would the maximal number of items/pairs be different for leaf nodes? In both cases it is $n-1$ where $n$ is the order. – Hendrik Jan Dec 20 '17 at 14:46