I lost count, long ago, how many times a customer said this:
“You just have to measure one - they’re all the same size”.
Now, if you sense the presence of a tire-kicker, you might accept that, at least, temporarily. After all, an experienced eye can see that several windows are, probably, all similarly sized. To get a rough estimate quickly, I’ve done that.
On one consultation, the customer was adamant. She knew for a FACT that all the windows were exactly the same throughout her newly constructed home. She did not need me to waste my time or hers with measurements.
A quick look around contradicted her statement. There were at least 3 completely different window sizes in the home, to say nothing of the variation that is inevitably present between two windows of the ‘exact’ same size.
Even a ¼” difference can ruin your day so why risk it?