The punishment in the grave may happen to sinners among those who affirm the Oneness of Allah; the squeezing in the grave will happen to everyone

Praise
be to Allah.

Firstly: 

There is
no contradiction, praise be to Allah, between the texts that speak of the
punishment and blessing in the grave; all of them are true. What has been
narrated about the grave of the believer being widened seventy cubits by
seventy and illuminated for him, and its being said to him, “Sleep like the
bridegroom who will not be wakened except by the dearest of his family to
him,” and it being filled with green for him – as was narrated by
at-Tirmidhi (1071) and others, and classed as hasan by al-Albaani in
Mishkaat al-Masaabeeh – this has to do with the perfect believer who
would hasten to obey Allah and would be slow to disobey Allah, or is one of
those for whom Allah, may He be glorified and exalted, decrees salvation
from the punishment and trial of the grave, such as the martyrs. 

With
regard to what was narrated about the punishment of some Muslims in their
graves, this applies to the sinners who mixed righteous deeds with bad
deeds. Allah may punish them in their graves for their sins, and in the Fire
on the Day of Resurrection until, when they have been cleansed and purified,
He will grant permission for them to enter Paradise, as is proven in
Saheeh al-Bukhaari, 7047, from the hadeeth of Samurah ibn Jundub (may
Allah be pleased with him), that the punishment of the grave will be for
many of the sinners among those who affirmed the Oneness of Allah, such as
those who slept and missed obligatory prayers, or those who committed zina,
consumed riba (usury) and liars whose lies spread far and wide. 

Al-Haafiz
Ibn Hajar said: 

This
indicates that some sinners will be punished in al-barzakh.

End quote
from Fath al-Baari, 12/445 

The
punishment in the grave is also proven for the one who does not take
precautions to avoid his urine (getting on his clothes and body) and the one
who goes about spreading malicious gossip among people, as it says in
al-Bukhaari, 216; and Muslim, 292. 

Ibn
al-Qayyim (may Allah have mercy on him) said: 

The
punishment in the grave is of two types: one type that is ongoing, apart
from that which is narrated in some hadeeths about it being reduced for them
in the period between the two trumpet blasts, then when they rise from their
graves they will say: ‘Woe to us, who has raised us up from our resting
place?’. The fact that it will be ongoing is indicated by the verse in which
Allah, may He be exalted, says (interpretation of the meaning): “The
Fire; they are exposed to it, morning and afternoon” [Ghaafir 40:46]. 

The second
type will last for a while and then cease. This is the punishment of some
sinners whose sins were minor. They will be punished according to their
sins, then it will be reduced, as they will be punished in the Fire for a
while, then the punishment will cease. The punishment may be stopped for
them by virtue of supplication (du‘aa’), charity, prayers for forgiveness or
the reward for Hajj (if these actions are performed by relatives or others
after their death).

End quote
from ar-Rooh, p. 89 

For
information on some forms of punishment in the grave, please see the answer
to question no. 8829

Secondly: 

There is a
difference between the punishment in the grave that will affect the sinners
and that with which the believer will be tested in his grave of squeezing
and the questions of the two angels. This is not a punishment; the fear and
dread of the grave, and the squeezing, are things that will happen to
everyone;, even the righteous among the believers will experience some of
that. 

With
regard to punishment in a specific sense, this is what we referred to in the
first paragraph of this answer; it is a punishment for specific things, and
is not something general that applies to everyone. 

As-Suyooti
(may Allah have mercy on him) said in his commentary on an-Nasaa’i (4/103): 

An-Nasafi
said: The obedient believer will not have any punishment in the grave, but
he will experience the squeezing of the grave. End quote. 

This is
explained further by the report narrated by Ahmad (23762) from ‘Aa’ishah,
from the Prophet (blessings and peace of Allah be upon him) who said: “There
is squeezing in the grave and if anyone were to be saved from it, Sa‘d ibn
Mu‘aadh would have been saved from it.”

Claased as
saheeh by al-Albaani in as-Saheehah, 1695 

This
squeezing is the first thing experienced by the deceased when he is placed
in his grave; it is not part of the punishment of the grave which will
happen to the sinners among the Muslims, based on the fact that it happened
to Sa‘d ibn Mu‘aadh (may Allah be pleased with him) at whose death the
Throne of the Most Merciful shook, as is proven in al-Bukhaari, 3803; and
Muslim, 2466 

For more
information on that, please see the answers to questions no.
71175 and 142853

Thirdly: 

The words
of the questioner, “each cubit is one foot six inches”, concerning the
length of the cubit mentioned in the hadeeth, “his grave will be widened for
him seventy cubits” is something for which there is no evidence, because the
life of al-barzakh is part of the unseen that we believe in, but we cannot
measure it by worldly standards. We believe that the grave of the believer
will be widened for him seventy cubits, but we do not speak about the length
of these cubits, because that is part of the unseen. The hadeeth of al-Bara’
that was narrated by Imam Ahmad (18063) concerning that says: “his grave
will be widened for him as far as his eye can see.” Classed as saheeh by
al-Albaani in Saheeh al-Jaami‘, 1676. 

And Allah
knows best.