As a rule, doors are 'glazed' (installed) from the inside and windows from the outside

'Tight' size refers to the dimensions of the
 aperture into which the glass is to be fitted.

To ensure a good fit, glass size is generally
  3 to 4mm less overall than tight size.

Extra care should be taken with old   unsquare  frames

If possible remove the putty or bead
so that sizes can be checked.

We need to know the visible size if your panels are to have a border.

Please see 'Critical Locations' regarding
safety glass