Между шкафом и дверью осталось полметра.

Because the preposition между normally takes the instrumental case in modern Russian.

So:

• шкаф → шкафом
• дверь → дверью

The phrase между шкафом и дверью means between the wardrobe/cabinet and the door.

A useful pattern to remember:

• между столом и окном
• между домом и рекой
• между мамой и папой

Both nouns after между stay in the same case.

Because дверь is a feminine noun of the third declension, and its instrumental singular ends in -ью.

So the forms are:

• nominative: дверь
• genitive: двери
• dative: двери
• accusative: дверь
• instrumental: дверью
• prepositional: двери

Since между needs the instrumental here, дверью is the correct form.

In sentences about an amount, distance, or quantity left, Russian very often uses neuter singular past tense:

• осталось полметра
• осталось пять минут
• осталось два вопроса

Here полметра is treated as a remaining amount, not as an ordinary subject like a person or object acting on its own.

So осталось is the normal form, even though метр itself is masculine.

Because пол- in this meaning is followed by the genitive singular of the noun.

So:

• метр → полметра
• час → полчаса
• килограмм → полкилограмма

That is the standard Russian way to say half a meter, half an hour, etc.

You can also say половина метра, but полметра is shorter and more natural in everyday speech for measurements.

Here осталось means remained or was left.

So the sentence is saying that after placing or measuring something, the space left between the two objects was half a meter.

This verb often appears in situations like:

• осталось десять минут — ten minutes were left
• осталось мало места — little space was left
• остался один вопрос — one question remained

In this sentence, it refers to the remaining distance/gap.

Because Russian does not need a dummy subject like English there in sentences such as there was or there remained.

English says:

• There was half a meter left.

Russian simply says:

• Осталось полметра.

This is very normal. Russian often leaves out words that English needs for sentence structure.

The difference is aspect.

• осталось = perfective
• оставалось = imperfective

In this sentence, осталось sounds like a result: in the end, half a meter was left.

оставалось would sound more like:

• it was remaining at that time
• that was the amount left in an ongoing situation
• background description rather than a finished result

So:

• Между шкафом и дверью осталось полметра = in the end, the gap turned out to be half a meter.
• Между шкафом и дверью оставалось полметра = there was half a meter left at that point / in that situation.

Yes. Russian word order is flexible, and changing it changes the focus more than the basic meaning.

The given sentence:

• Между шкафом и дверью осталось полметра.

This sounds natural and starts with the location.

You could also say:

• Осталось полметра между шкафом и дверью.

That version puts more attention on полметра as the important new information.

So the original order is very natural, but it is not the only possible order.

Not always. Шкаф is a broad word for a tall piece of furniture used for storage.

Depending on context, it can be translated as:

• wardrobe
• cabinet
• cupboard
• sometimes closet in looser translation

So in a sentence like this, the exact English word depends on what kind of шкаф the speaker has in mind.