The number is not a property of your deployment tool. It is your server's available memory divided by what one build takes at its peak, and every answer that skips that division is guessing on your behalf.
So do the division. An install-and-build of a Next.js, Nuxt, Remix or React Router project wants roughly 2 GB of RAM while it runs.
That number is worth being honest about: it comes from running these deploys rather than from a benchmark, and the observation behind it is sharper than the average. On servers with 2 GB of RAM or less, the build fails — not sometimes, and not only under load. Above that the figure is a starting point you should replace with your own, measured the way the next section describes. But the floor is not a rule of thumb.
Once you have a number, the rest is arithmetic:
concurrent builds = (RAM available while the site is serving − headroom) ÷ peak RAM per build
