PHP accurate string length

We have a field in mysql where the data is stored like the following: a:4:{i:0;a:5:{s:6:"object";s:9:"ZnSection";s:7:"options";a:27:{s:11:"top_padding";s:1:"0";s:14:"bottom_pa.... What we want to do is get an accurate cound of each part and update the character counter. For example the part s:6:"object" means object has 6 characters, if we change that to s:6:"objects" the s6 will become s7 We have this working but some of the text is html and line breaks which give an inaccurate count of the characters. Please do not suggest strlen or stripping the HTML as that is needed. More details or a demo can be shown to the selected worker.