This paper introduces a typometric measure of flexibility, which quantifies the variability of head-dependent word order on the whole set of treebanks of a language or on specific constructions. The measure is based on the notion of head-initiality and we show that it can be computed for all of languages of the Universal Dependency treebank set, that it does not require ad-hoc thresholds to categorize languages or constructions, and that it can be applied with any granularity of constructions and languages. We compare our results with Bakker’s (1998) categorical flexibility index. Typometric flexibility is shown to be a good measure for characterizing the language distribution with respect to word order for a given construction, and for estimating whether a construction predicts the global word order behavior of a language.