
Are you mounting your hinges on the rear of the gate post?
As the hinges are mounted on the back of the post you do not need to reduce any size from your lowest measurement. The gate will open inwards towards property.

Are you mounting hinges between the gate posts?
If you're mounting hinges to the inner face of the posts, this allows the gate to open both ways.
To purchase the correct size gate for this, you need to take 140mm away from your smallest measurement of the three. That's your gate width.