A Tennis court is denoted as an overall figure because it does include runbacks and sides.

The actual court is one size - the actual overall size which includes runbacks is greater.
21 feet either end is the longest runback for a championship court
The courts is 78 feet long, 21 + 21 is 42, add 42 to 78 and you have the length of a championship court (i.e. 120 feet)

The ‘Over-Sized’ Court
But there is a larger one for grand slams but not all the courts have it only the centre court and number one court are larger than championship size.
So when you get to a certain level your movements and what you are able to do…
A championship court is a handicap. And so as the players come through, so you find that the better players win at Wimbledon, because they use the whole of the court and yet its oversized compared to the average court at Wimbledon.
So, you always know when you’ve got a good player because he performs his best on centre court or number one.
They let everyone have a go at it just to see what it’s like – it’s a form of training.

Wimbledon Nearly Slips Up
Wimbledon organise things in an incredible way with an awful lot of knowledge attached to it because they bring the players onto the courts and in my experience did they fail..
And that was an unseeded player got almost to a final and he hadn’t played on number 1 or centre court, which was really unfair. So what they did was they broke their rules and they let him play on in the morning before his match I think it was a semi final
And they allowed him to practice on centre court which is a forbidden thing.
So they overcame the problem that way because he could have said I’m not playing until you’ve let me use the court – he probably did. So only once did they fail.
So there is this oversize which relates to the show courts of the Grand Slam area. They have it. You go to Australia – the main attraction courts, the show courts – are normally oversized to the championship court as stipulated in rules.

The Service Line
The Service Line is positioned 6 yards from the baseline and 7 yards from the net.
This sometimes is confused. I have known courts to get them the wrong way round, which means that the service court could if not marked out properly to be very difficult to get the ball into. I have known it happen!

The Net
The net is 3 foot high at the centre strap and 3 foot 6 inches high at the net posts. This means that the net sags towards the centre. So it’s harder to hit down the line than it is across the court, which is why people who try to pass down the line sometimes have a problem – because they don’t make allowance for the height of the net at the side.