Если я сегодня всё измерю и запишу размеры, завтра мы купим только то, что точно поместится в новую квартиру.

These are perfective verbs, and in Russian perfective verbs do not have a true present tense. Their “present-looking” forms actually refer to the future.

So:

• измерю = I will measure
• запишу = I will write down
• купим = we will buy
• поместится = it will fit

This is very common in Russian. Compare:

• измеряю = I am measuring / I measure (imperfective, present)
• измерю = I will measure (perfective, future)

Because the sentence talks about completed actions and results:

• измерю — I will finish measuring
• запишу размеры — I will write the measurements down
• купим — we will make the purchase
• поместится — it will successfully fit

Perfective aspect is natural when the speaker has specific, goal-oriented actions in mind.

If you used imperfective verbs instead, the sentence would sound more like focusing on the process or repeated action, not on the completed result.

They describe two separate completed actions:

1. измерю = I will measure everything
2. запишу размеры = I will write down the measurements

Russian often states both actions clearly, because measuring something and recording the results are not the same thing.

So the sentence means something like:

• First, I’ll measure everything.
• Then I’ll note down the dimensions.
• Tomorrow, we’ll buy only what will definitely fit.

Because they refer to different things:

• всё = everything (all the relevant items / spaces / walls / furniture / rooms, depending on context)
• размеры = the measurements / dimensions

So измерю всё means measure everything, while запишу размеры means write down the dimensions.

It is not repetitive in Russian; it is perfectly natural.

Размеры is the plural of размер.

Depending on context, it can mean:

• measurements
• dimensions
• sizes

In this sentence, записать размеры is a very natural phrase meaning to write down the dimensions/measurements.

То, что is a very common structure meaning:

• that which
• what
• the thing(s) that

In this sentence:

• только то, что точно поместится = only that which will definitely fit / only what will definitely fit

It is often used when English would simply say what.

For example:

• Я куплю то, что мне нужно. = I’ll buy what I need.
• Literally: I’ll buy that which I need.

Because поместится is perfective and refers to a single successful result in the future: something will fit.

• поместится = will fit / will be able to fit
• помещается = fits / is fitting (describes a current or habitual situation)

Here the speakers are deciding what to buy tomorrow, based on whether it will fit in the new apartment. That makes the future perfective form the natural choice.

Also, поместиться often implies fitting with enough room, successfully, or within limits.

Because this sentence implies motion or placement into the apartment.

With в:

• в + accusative = into / direction toward
• в + prepositional = in / location

So:

• в новую квартиру = into the new apartment
• в новой квартире = in the new apartment

Here, поместится в новую квартиру means will fit into the new apartment.

Because after в with a meaning of direction/movement, Russian uses the accusative.

The base form is:

• новая квартира = nominative

After в with motion:

• в новую квартиру = accusative

This happens because the idea is not just location, but fitting into that space.

Точно here means:

• definitely
• for sure
• exactly / certainly

In this sentence, it strengthens the idea that they want to buy only things that they are sure will fit.

So:

• что точно поместится = that will definitely fit

It adds a practical, careful tone.

Because только modifies the whole object phrase:

• только то, что точно поместится = only what will definitely fit

This is the most natural placement in Russian.

If you move только, the emphasis can change. Russian word order is flexible, but this version is straightforward and neutral.

Russian punctuation requires commas here because there are subordinate clauses.

1. Если я сегодня всё измерю и запишу размеры,
   This is an if-clause, so it is separated from the main clause by a comma.

2. только то, что точно поместится...
   Here что точно поместится в новую квартиру is a relative/subordinate clause describing то, so it also takes a comma.

Russian uses commas with subordinate clauses more consistently than English does.

It sounds like a real, practical condition, not an unlikely hypothetical.

The speaker means something like:

• If I measure everything today and write down the dimensions, then tomorrow we’ll buy only what will definitely fit.

There is no бы, so this is not a “would” type of conditional. It is more like a plan.

Grammatically, you could say буду измерять, but it would change the nuance.

• измерю = I will measure it all and finish
• буду измерять = I will be measuring / focus on the process

In this sentence, the result matters: the measurements need to be completed today so they can buy things tomorrow. That is why измерю is better.

The same logic applies to запишу rather than буду записывать.

Yes, the word order is natural and neutral.

Russian word order is flexible, but this version flows well:

• condition first: Если я сегодня всё измерю и запишу размеры
• result next: завтра мы купим только то...

You could move some words for emphasis, for example:

• Если я сегодня измерю всё и запишу размеры...
• Завтра мы купим только то, что в новую квартиру точно поместится.

These are possible, but the original sentence sounds clear and standard.