die Länge
length
The spatial extent of an object from one end to the other.
Die Länge des Tisches beträgt genau zwei Meter.
The length of the table is exactly two meters.

length
Loading your saved state.
length
The spatial extent of an object from one end to the other.
Die Länge des Tisches beträgt genau zwei Meter.
The length of the table is exactly two meters.

'Die Länge' (length) is the noun related to the adjective 'lang' (long). It describes the property or measurement of how long something is. If you know 'lang' (long), you can easily work out 'Länge' (length).
Wie lang ist der Tisch? – Die Länge des Tisches ist zwei Meter.
How long is the table? – The length of the table is two meters.
The meaning of 'Länge' (length) becomes clear from context. In connection with units of measurement such as 'Meter' (meters) or 'Kilometer' (kilometers), it refers to spatial extent. With time expressions such as 'Stunden' (hours), or in the context of films and lectures, it refers to duration.
Die Länge der Brücke ist beeindruckend.
The length of the bridge is impressive.
To state the exact length or duration of something, the preposition 'von' (of) is often used. The typical structure is 'eine Länge von + [Zahl und Einheit] haben' (to have a length of + [number and unit]).
Das Seil hat eine Länge von zehn Metern.
The rope has a length of ten meters.
In the fixed expression 'etwas in die Länge ziehen' (to drag something out), 'etwas' (something) is always the accusative object. It names the thing that is intentionally or unintentionally being prolonged.
Er versucht, das Gespräch künstlich in die Länge zu ziehen.
He is trying to artificially drag out the conversation.
In a geographic context, 'Länge' (longitude) or 'Längengrad' (degree of longitude) almost always appears together with its counterpart 'Breite' (latitude) or 'Breitengrad' (degree of latitude). The two words form a fixed pair for determining positions on Earth.
Der Navigator berechnete die genaue Länge und Breite ihrer Position.
The navigator calculated the exact longitude and latitude of their position.
In the meaning 'langweiliger Abschnitt' (boring section/slow passage), the word is almost always used in the plural: 'Längen' (slow passages). For example, people speak of a film or book that 'Längen hat' (has slow passages).
Das Buch ist spannend, hat aber leider einige Längen im Mittelteil.
The book is exciting, but unfortunately it has a few slow passages in the middle section.
height / amount
'die Höhe' and 'die Länge' both describe a spatial extent. The difference is the direction. 'die Höhe' means the distance from bottom to top, for example with a cabinet, a tree, or a building. 'die Länge' means the distance from one end to the other, often horizontally or along a line. Learners may confuse the words because both are measurements. A practical tip: if you ask 'Wie hoch?' (How high?), it is about 'Höhe'. If you ask 'Wie lang?' (How long?), it is about 'Länge'.

Vor dem Kauf misst ihr die Länge des Tisches im Wohnzimmer.
Before buying it, you measure the length of the table in the living room.
Die Höhe des Regals passt genau unter die Decke.
The height of the shelf fits exactly under the ceiling.