Portable R for Windows + Rtools – TheCoatlessProfessor

Abstract

Portable R for Windows now offers an R + Rtools variant that bundles the full Rtools compilation toolchain alongside R. Extract it, and install.packages(type = "source") works out of the box. No installer, no system PATH changes, no registry entries. Available for R 4.3.0 through 4.5.3, x64 and ARM64.

Portable R for Windows now has a new variant that bundles the full Rtools compilation toolchain alongside R. Download, extract, and install.packages(type = "source") works immediately. No installer, no system PATH changes, no registry entries. This post covers what’s in the bundle, how R discovers the toolchain, and as a bonus from digging through R’s source code for this project, how to point any R installation at a custom Rtools location.

R only vs. R + Rtools

The original R-only variant (~100 MB .zip) still covers the majority of use cases where CRAN binary packages are sufficient. The new R + Rtools variant (~850 MB .7z) is for when you need a C/C++/Fortran compiler: packages without CRAN binaries, development versions from GitHub, or ARM64 Windows where CRAN doesn’t distribute binaries at all.

They’re separate downloads because Rtools is large. The full toolchain is ~3.5 GB uncompressed, so bundling it by default would turn a quick 100 MB download into something much heavier. The R + Rtools variant uses .7z (LZMA2) instead of .zip because the combined bundle exceeds GitHub’s 2 GB release asset limit under zip compression. LZMA2 brings it down to ~850 MB.

Instead of installing Rtools separately (which touches the registry, modifies PATH, and installs to C:\rtools45), the -full variant embeds it directly inside the portable R directory. R finds the bundled toolchain through RTOOLS{VER}_HOME (or RTOOLS{VER}_AARCH64_HOME on ARM64), set in etc/Renviron.site. This tells R’s Makeconf where to find compiler headers and libraries, and tells Rcmd_environ and Rprofile.windows where to find gcc, make, and the rest of the toolchain. Everything resolves relative to R_HOME, so the whole directory is relocatable.

Quick start

Download and extract the R + Rtools bundle (requires 7-Zip for the .7z format):

# Install 7-Zip if needed: winget install 7zip.7zip
curl.exe -fSLO https://github.com/portable-r/portable-r-windows/releases/download/v4.5.3/portable-r-4.5.3-win-x64-full.7z
& "$env:ProgramFiles\7-Zip\7z.exe" x portable-r-4.5.3-win-x64-full.7z

Then compile from source:

portable-r-4.5.3-win-x64-full\bin\Rscript.exe -e "install.packages('Rcpp', type='source')"

Windows 11 desktop showing three windows: a PowerShell terminal compiling the Rcpp package from source using g++ from the bundled Rtools45 toolchain, a File Explorer window showing the portable-r-4.5.3-win-x64-full directory containing R files alongside an rtools45 folder, and a second Explorer window showing the library folder with Rcpp and other installed packages. — Windows 11 showing PowerShell compiling Rcpp from source using the bundled Rtools45 toolchain, with File Explorer showing the portable R directory structure including the rtools45 folder and the library with installed packages.

What’s in the box

Rtools lives inside the R tree as a rtools{VER}/ subdirectory. Renviron.site sets RTOOLS45_HOME to point at it, and R’s build infrastructure derives everything else from that.

Diagram showing the portable R directory structure with R components in blue and Rtools components in amber. Renviron.site sets RTOOLS45_HOME, Makeconf reads it for compiler flags, and the result is self-contained source package compilation. — Portable R + Rtools directory layout showing how Renviron.site and Makeconf connect to the bundled rtools45 directory.

Each R minor version maps to the correct Rtools version automatically:

R Series	Rtools	Compiler
R 4.5.x	Rtools45	GCC 14.3 (x64), LLVM/Clang 19 (ARM64)
R 4.4.x	Rtools44	GCC 13.3 (x64), LLVM/Clang 17 (ARM64)
R 4.3.x	Rtools43	GCC 12.3 (x64)

Archive format

The R-only variant remains a .zip (~100 MB) that Windows can extract natively. The R + Rtools variant is distributed as .7z (~850 MB) because the full toolchain is ~3.5 GB uncompressed, which exceeds GitHub’s 2 GB release asset limit under zip compression. LZMA2 gets it down to a manageable size. 7-Zip is free, open source, and available via winget install 7zip.7zip.

Available versions

All 12 supported R versions (4.3.0 through 4.5.3) have R + Rtools variants available for x64. ARM64 variants are available for R 4.4.0+. See the full download table on the releases page.

Staying current

A daily CI job scrapes CRAN for new R and Rtools releases. When a new version appears, the build system updates automatically and publishes new releases. The download table in the README is generated from the actual GitHub releases, so it always reflects what’s published.

Using Rtools from a custom location

If you’re not using the portable R + Rtools bundle but want to install Rtools somewhere other than the default C:\rtools45, R provides environment variables to point it at a custom location. This is useful if you keep Rtools on a secondary drive, a network share, or alongside a project.

The short version

Set RTOOLS{VER}_HOME to the root of your Rtools installation, where {VER} matches your R series (e.g., RTOOLS45_HOME for R 4.5.x, RTOOLS44_HOME for R 4.4.x, RTOOLS43_HOME for R 4.3.x). R’s Makeconf, Rcmd_environ, and Rprofile.windows all derive their compiler flags, include paths, library paths, and PATH from this single variable.

More precisely, the variable name is RTOOLS{VER}_{ARCH}_HOME where {ARCH} is empty for x64 and AARCH64 for ARM64. So on x64 you set RTOOLS45_HOME, and on ARM64 you set RTOOLS45_AARCH64_HOME. The ARM64 section below covers this in detail.

System-wide (persistent, affects all R sessions):

[System.Environment]::SetEnvironmentVariable("RTOOLS45_HOME", "D:\tools\rtools45", "User")

Per-session (temporary, current terminal only):

$env:RTOOLS45_HOME = "D:\tools\rtools45"

Per-project (via .Renviron in your project root):

RTOOLS45_HOME=D:/tools/rtools45

Note the forward slashes in .Renviron files. R handles them correctly on Windows.

What this controls

Flow diagram showing RTOOLS45_HOME at the top flowing into three R components: Makeconf for compiler flags, Rcmd_environ for R CMD PATH, and Rprofile.windows for interactive PATH. All three converge into package compilation working. — How RTOOLS45_HOME flows into Makeconf, Rcmd_environ, and Rprofile.windows to enable package compilation.

When R compiles a package from source, three things need to find Rtools:

Makeconf needs the toolchain’s include and library directories for -I and -L compiler flags. It reads RTOOLS45_HOME and derives LOCAL_SOFT from it (e.g., D:/tools/rtools45/x86_64-w64-mingw32.static.posix).
Rcmd_environ needs the toolchain’s bin/ directories on PATH so R CMD can find gcc, make, etc. It reads RTOOLS45_HOME and constructs R_RTOOLS45_PATH from it.
Rprofile.windows does the same PATH setup for interactive R sessions (RGui, RTerm).

All three read from the same RTOOLS{VER}_HOME variable, so setting it once is sufficient.

ARM64

ARM64 Windows uses a separate variable: RTOOLS45_AARCH64_HOME (or RTOOLS44_AARCH64_HOME). The default is C:\rtools45-aarch64. If you’ve installed the ARM64 Rtools elsewhere:

$env:RTOOLS45_AARCH64_HOME = "D:\tools\rtools45-aarch64"

Alternative: `R_CUSTOM_TOOLS_SOFT`

If you need finer control, R_CUSTOM_TOOLS_SOFT overrides LOCAL_SOFT in Makeconf directly, taking precedence over RTOOLS{VER}_HOME. Point it at the toolchain’s sysroot (not the Rtools root):

R_CUSTOM_TOOLS_SOFT=D:/tools/rtools45/x86_64-w64-mingw32.static.posix

Similarly, R_CUSTOM_TOOLS_PATH overrides the PATH that Rcmd_environ and Rprofile.windows construct:

R_CUSTOM_TOOLS_PATH=D:/tools/rtools45/x86_64-w64-mingw32.static.posix/bin;D:/tools/rtools45/usr/bin

These are built into R’s source code (src/gnuwin32/fixed/etc/Makeconf, src/gnuwin32/fixed/etc/Rcmd_environ, and src/library/profile/Rprofile.windows) and are the official mechanism for non-standard Rtools locations.