die Gesamtlänge
total length
The entire extent of an object, route, or period of time from beginning to end.
Die Gesamtlänge der chinesischen Mauer beträgt über 21.000 Kilometer.
The total length of the Great Wall of China is over 21,000 kilometers.

total length
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total length
The entire extent of an object, route, or period of time from beginning to end.
Die Gesamtlänge der chinesischen Mauer beträgt über 21.000 Kilometer.
The total length of the Great Wall of China is over 21,000 kilometers.

This word is a clear compound of 'gesamt' (total, whole) and 'die Länge' (length). So it literally means the 'whole length.'
Bitte messen Sie die Gesamtlänge des Tisches.
Please measure the total length of the table.
There are two typical sentence patterns. Either 'die Gesamtlänge' (the total length) is the subject ('Die Gesamtlänge beträgt …' — The total length is …), or it is attached to another noun with 'von' ('… mit einer Gesamtlänge von …' — with a total length of …).
Die Brücke hat eine Gesamtlänge von zwei Kilometern.
The bridge has a total length of two kilometers.
'Gesamtlänge' is often used for geographic objects, structures, or media. Typical examples are the total length of a river, a route, a bridge, or a film.
Die Gesamtlänge der Wanderroute ist für Anfänger zu anspruchsvoll.
The total length of the hiking route is too demanding for beginners.
route / distance
'die Strecke' and 'die Gesamtlänge' can both have to do with length. However, 'Strecke' means the route or section itself that you walk, drive, or describe. 'Gesamtlänge' means the whole measured length from beginning to end. That can be the length of a route, but also the length of an object or a text. The words can be confused when you want to know how long a route is. In that case, the Strecke is the route; the Gesamtlänge is the number or information about its length.

Die Gesamtlänge des Radwegs beträgt fast vierzig Kilometer.
The total length of the bike path is almost forty kilometers.
Die Strecke durch den Wald ist schön, aber nach Regen sehr matschig.
The route through the forest is beautiful, but very muddy after rain.