• Windows
  • Games

Unreal's derived data cache is bigger than the engine

Engine installs, DDC and per project intermediates. The three folders that make Unreal the largest thing on a PC.

5 min read

Unreal is the largest development install most Windows machines ever see. An engine version is tens of gigabytes, the derived data cache can exceed it, and every project keeps its own intermediates on top.

The three places

Get-ChildItem 'C:\Program Files\Epic Games' -Directory -EA SilentlyContinue | ForEach-Object {
  $s = (Get-ChildItem $_.FullName -Recurse -Force -File -EA SilentlyContinue | Measure-Object Length -Sum).Sum
  [PSCustomObject]@{ GB = [math]::Round($s/1GB,2); Engine = $_.Name }
}
Get-ChildItem "$env:LOCALAPPDATA\UnrealEngine" -Directory -EA SilentlyContinue | ForEach-Object {
  $s = (Get-ChildItem $_.FullName -Recurse -Force -File -EA SilentlyContinue | Measure-Object Length -Sum).Sum
  [PSCustomObject]@{ GB = [math]::Round($s/1GB,2); Path = $_.FullName }
}
WhatWhereRegenerated
Engine installsProgram Files\Epic Games\UE_5.xBy reinstalling
Shared DDC%LOCALAPPDATA%\UnrealEngine\Common\DerivedDataCacheYes, by rebuilding
Project DerivedDataCacheIn the projectYes
Project IntermediateIn the projectYes
Project SavedIn the projectLogs and autosaves, mostly yes
Project BinariesIn the projectYes, by compiling

The derived data cache

DDC holds the cooked, platform specific versions of every asset: shaders, textures, meshes. It exists so that opening a project does not mean recooking everything, and it is entirely derived from the source assets. Deleting it costs a long first open and nothing else.

Cleaning a project properly

  1. Close the editor.
  2. Delete Intermediate, Saved, DerivedDataCache and Binaries from the project folder.
  3. Right click the .uproject and choose Generate Visual Studio project files.
  4. Open it again and let it rebuild.

That is the standard fix for a misbehaving project as well as a cleanup, which is why it is worth knowing. Content, Config and Source are the project; everything else in that folder is generated.

Engine versions you no longer open

Each engine install is tens of gigabytes and the Epic launcher keeps every version you have added. Removing one through the launcher is the supported route, and projects pinned to it will ask for it again if you open them.

Common questions

What is the DerivedDataCache in Unreal?

Cooked, platform specific versions of every asset, kept so opening a project does not recook everything. It is derived from the source assets, so deleting it costs a long first open and nothing else.

Which Unreal project folders are safe to delete?

Intermediate, Saved, DerivedDataCache and Binaries are all generated. Content, Config and Source are the project itself and must be kept.

How much space does Unreal Engine use?

Each engine version is tens of gigabytes, the shared derived data cache can exceed that, and each project keeps its own intermediates. It is usually the largest development install on a PC.

How do I remove an old Unreal engine version?

Through the Epic Games Launcher, which is the supported route. Projects pinned to that version will offer to reinstall it if you open them again.

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