How does one get the 401(k) max contribution of 57K?

I think the currently accepted answer misses the most typical way that larger contributions can be made. The $19.5k limit applies to employee pre-tax and Roth contributions. Employee after-tax contributions are not subject to this limit, and can be used to reach the $57k total. After-tax contributions sound like a bad deal (contributions taxed going in and earnings taxed coming out), but in some 401(k) plans they can be converted to Roth balances, known as a mega backdoor Roth.

The modestly compensated "average Joe" can also get near that number by contributing the max $19,500, getting the 100% employer match of $19,500, the 5% employer match of say $4000... (we're up to $43,000 so far)...

...and then, make it a Roth 401(k) instead of a traditional.

A dollar in a Roth 401(k) is worth more than a dollar in a traditional, because you're bot having to bring the tax money into the retirement account. The taxes are paid externally to the account, and the money in it is all yours. If you're in a combined (state + Federal) tax bracket of 28%, $1.00 in a Roth is worth $1.39 in a Traditional.

(After you pay 28% taxes on $1.39, you are left with $1.00).

So that $43,000 Roth contrib is as good as a $59,722 Traditional contrib.

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"But wait, Harper! The employer contrib doesn't go into a Roth 401K, it goes into a traditional! That is to say, the employer doesn't pay the tax for you!"

Right, you have to pay that tax, by doing a Roth conversion inside the 401K. If they contrib'd $23,500, you convert that to Roth.

The $23,500 is transmuted into Roth funds inside the 401K. However, the taxes on this event are paid outside the 401K. Get it? You pay $6,580 in tax, but your 401K becomes worth $6,580 more because it is now post-tax money. It's a left-handed way of contributing $6,580 additional into the 401(K). Just instead of writing the check to Fidelity today and a check to the IRS at retirement, you write a check to the IRS today and the value pops into your account. It's not a free lunch, but it provides the high dollar value of contrib that you are seeking.

There are several different types of contributions an employer can make to a 401(k), but the main types are "matching" and "profit sharing". Matching is tied to contributions the employee makes, while profit sharing contributions are independent of that. The limiting factor is the rule that the total employer contribution to your 401(k), matching and profit sharing combined, cannot exceed 25% of your salary.

With the current maximum being $57,000, and supposing you make the maximum individual contribution $19,500, you still need the company to contribute (in one way or another) $37,500 to your 401(k), which means you have to make at least $150,000 in salary. And have an employer with a very, very generous company 401(k) contribution.

In addition to the other great answers, allow me to present one from the perspective of a self-employed individual:

I am a self employed individual with a Solo 401(k). I am able to make contributions as both employee and employer even though the contributions are coming from basically the same pool of money.

As an employee, I can contribute up to $19,500 dollars. That's the same as as in the other answers. That's $37,500 short of the limit you're asking about.

As my own employer, I can also contribute up to a certain limit. I need to subtract one half of my self employment tax and also subtract my employee 401k contributions from my total compensation - then I can contribute up to 25% of that amount to the 401k. To make a $37,500 employer contribution I would (very very roughly) need to be earning $200,000 or more a year.

See this document from the IRS for more information on how the limits of the employer portion are calculated.