How do I measure replacement glass for this window?

Just like it sounds. I need to replace this window pane at the church. I don't know how to measure it, not which side to take the trim from to get it out and in. Help?

Daylight plus 1/2".

And most older wood windows are pointed in from the exterior with a glazing putty. The glass is held in with glazing points while the putty is applied and sets up. All of that should be available at a hardware store or Lowes. They can also cut the glass for you. 

you are going to need to pull the interior trim around the edge anyway , 

so do that and measure the opening , 

also check that the hole is "square" , the building could have moved thru the years,  

7 1/2x11 1/4.  Interior wood will pop off, that's not set with putty.  

If it is putty I'd be under conviction using these glazing points at the house of the Lord.  (JK)

I know about the points and putty. One vote for remove exterior trim and some votes for removing the interior trim??

The exterior is not trim.  It's one piece with the mullions and sash frame.  The inside slanty pieces pop off, you set the new glass in whatever sealant you want(i would use clear alex plus caulk) and put the inside trims back. 
 

I didn't stay a holiday inn express last night, but i have been installing and repairing windows for 25 years

Patrick (Forum Supporter) said:

The exterior is not trim.  It's one piece with the mullions and sash frame.  The inside slanty pieces pop off, you set the new glass in whatever sealant you want(i would use clear alex plus caulk) and put the inside trims back. 
 

I didn't stay a holiday inn express last night, but i have been installing and repairing windows for 25 years

I did this on my basement window and it worked out fine. I steal waffles from a Holiday Inn Express' I don't stay at and had no experience installing glass. 

Patrick (Forum Supporter) said:

The exterior is not trim.  It's one piece with the mullions and sash frame.  The inside slanty pieces pop off, you set the new glass in whatever sealant you want(i would use clear alex plus caulk) and put the inside trims back. 
 

I didn't stay a holiday inn express last night, but i have been installing and repairing windows for 25 years

Thanks!

Yum Doritos.

A little disappointed no one responded  "With a ruler".  Are any of you really dads? 

Nope!

It definitely disassembles from the outside. 

Toyman01 (Moderately Supportive Dude) said:

And most older wood windows are pointed in from the exterior with a glazing putty. The glass is held in with glazing points while the putty is applied and sets up. All of that should be available at a hardware store or Lowes. They can also cut the glass for you. 

 

 

Mostly winner. No points, just big fat trim nailed in.

Patrick (Forum Supporter) said:

The exterior is not trim.  It's one piece with the mullions and sash frame.  The inside slanty pieces pop off, you set the new glass in whatever sealant you want(i would use clear alex plus caulk) and put the inside trims back. 
 

I didn't stay a holiday inn express last night, but i have been installing and repairing windows for 25 years

you got it bass-ackwards though. The inside was one piece, the outside trim pieces pulled off.