Using it

  • Pick the language your project is mostly written in. Each one carries a baseline time and a parallel factor — how well its toolchain spreads work across cores.
  • Pick the processor. The tool uses its performance index and its core count.
  • Pick the project size: small is about 5,000 lines, medium about 50,000 and large about 500,000. If your project sits between two sizes, look at both results.

The baseline is the time a clean build of that size takes on a reference 6-core processor with an index of 5,000, roughly a Ryzen 5 5600. A faster processor divides it; more cores divide it again, but only as far as the language lets them.

More cores or a faster processor? It depends on the language

The parallel factor is the most important number on the page, and it varies more than people expect. C (0.95), C++ and Fortran (0.9) use almost every core you give them, because each source file compiles on its own. Rust (0.7) and Go (0.65) parallelise well but not perfectly: a crate or package has to wait for the ones it depends on. TypeScript (0.25) and JavaScript (0.2) barely benefit, since the classic TypeScript compiler type-checks a project on one thread. Python, Ruby, Perl and Lua (0.1) do almost no compiling at all.

  • Large C++ project (450 s baseline): a Ryzen 5 5600 takes about 7 min 39 s, a Ryzen 7 9800X3D (8 cores) 3 min 8 s, a Ryzen 9 9950X (16 cores) 1 min 40 s and a Core i7-14700K (20 cores) 1 min 38 s. Doubling the cores from the 9800X3D to the 9950X nearly halves the wait.
  • Large TypeScript project (85 s baseline): the 9800X3D takes about 43 s and the 9950X about 33 s. Twice the cores buys a quarter off, because the work does not spread.
  • Medium Rust project (65 s baseline): about 66 s on the Ryzen 5 5600 and 29 s on the 9800X3D.
  • Medium Go project (12 s baseline): about 12 s on the Ryzen 5 5600 and 3 s on the 9950X. Go builds are fast enough that a faster processor matters less than the cache does.

The practical reading: if you build C, C++ or Rust all day, core count is worth paying for. If you work in TypeScript or a scripting language, a fast 6- or 8-core processor gets you nearly all of the benefit, and the money is better spent on memory or a quieter machine.

What the estimate leaves out

It estimates clean builds. Most builds in a working day are incremental: one or two files change and the linker does most of the work. Those depend far more on single-thread speed and on the build system than on core count, and a good build cache can make them almost instant on any machine.

Every core counts the same. Intel's recent processors mix performance and efficiency cores, and the Core i7-14700K's 20 cores are 8 of one and 12 of the other, so the estimate flatters it. Treat close results between a hybrid Intel chip and an AMD one as a tie.

Memory and storage are assumed to keep up. A large C++ build wants roughly 2 GB of memory per parallel job; a machine that runs out starts swapping and every core waits. The baselines themselves are editorial estimates of typical projects, not measurements of a particular codebase, as the methodology page explains.

Before you buy

Compare two or three processors at your project's size rather than reading one result in isolation: the gap between them is more reliable than either absolute time. Then check the rest of the build — a 16- or 20-core processor under a long build draws a lot of power, which the power supply calculator sizes for, and the electricity calculator turns into a monthly cost.