Reduce Your Package Size and Fix Common Packaging Errors

Two normal problems, both fixable

If your last lesson ended with a packaging error in red text, or with a folder that's somehow several gigabytes for a tiny test level — welcome to the club. These are the two things that trip up almost everyone the first time they package a game, and neither means you did anything wrong. They mean Unreal is being careful: it would rather stop and tell you something is missing than silently ship a broken build.

The skill that fixes both is the same one: learning to read what Unreal is actually telling you in the Output Log instead of panicking at the wall of text. In this lesson we'll do exactly that — decode the log, fix the four errors that catch everyone, then turn to the second problem and trim a bloated package down to size. Plain English, no scary jargon.

First, where the truth lives: the Output Log

When packaging fails, Unreal usually pops up a small dialog that says something vague like 'Packaging failed. See the log for details.' That dialog is not the error — it's a pointer. The actual reason is in the Output Log.

Open it from the menu: Window → Output Log. It's a scrolling text panel of everything the engine is doing. When a package fails, the part you care about is near the bottom, and the useful lines are coloured: yellow for Warning, red for Error. The single most useful trick is to scroll to the bottom and read upward until you hit the first red Error line — that is almost always the real cause; everything below it is just fallout.

Fix the four errors that catch everyone

Each of these has a tell-tale phrase in the Output Log. Match the phrase, apply the fix. Tick them off as you confirm each isn't your problem.

1. ✓
   1Error mentions a missing or invalid reference

   Log phrase: something like 'can't find file', 'Failed to load', or a reference to an asset path that no longer exists. This happens when an asset was deleted or moved but something still points at it — a classic 'redirector' left behind by a rename.

   Fix: in the Content Browser, right-click the top-level Content folder and choose 'Fix Up Redirectors in Folder'. This cleans up stale rename pointers. If the log names a specific missing asset, find what references it (right-click the referencing asset → Reference Viewer) and either re-link it or delete the broken reference.

   TipRun 'Fix Up Redirectors in Folder' on the whole Content folder before every package. It's quick, harmless, and prevents a whole category of failures.

2. ✓
   2Error mentions an unset or missing Game Default Map

   Log phrase: a complaint about the 'Game Default Map' or 'startup map' being empty or invalid. A packaged game has no editor, so it needs to be told which level to load when it launches. If that slot is blank, packaging stops.

   Fix: go to Edit → Project Settings → Maps & Modes. Set 'Game Default Map' (the level the built game opens with) and 'Editor Startup Map' to a real, saved level from your project. Make sure the level is actually saved to disk first.

   TipWhatever level you set as the Game Default Map is what players see first — point it at your main menu or your playable level, not an empty test map.

3. ✓
   3Error mentions the platform SDK is not installed

   Log phrase: something like 'platform SDK not installed', or a build-tool error mentioning Visual Studio, the Windows SDK, or a compiler. To package for Windows, Unreal needs the platform build tools, even for a Blueprint-only project the first time it compiles.

   Fix: install the free Visual Studio Community with the 'Game development with C++' workload (which includes the Windows SDK Unreal needs). After installing, fully restart Unreal so it re-detects the tools. Epic's official 'Setting Up Visual Studio' page lists the exact components.

   TipThis one is a one-time setup per machine. Once the SDK is installed and detected, you won't see it again on that computer.

4. ✓
   4Error mentions a missing or cooking-failed asset

   Log phrase: 'Cook failed' followed by an asset name, or a warning that an asset couldn't be saved or compiled. Cooking is the step that converts your editor assets into the optimised form the packaged game uses; if one asset is corrupt or unsaveable, the cook stops.

   Fix: read the named asset in the log, open it in the editor, and re-save it (Ctrl + S). If it won't open or save, it may be corrupt — delete it and re-import or rebuild it. Then package again.

   TipSave everything before you package: File → Save All (Ctrl + Shift + S). A surprising number of 'cook failed' errors are just an unsaved asset.

5. ✓
   5Still stuck? Package again and re-read the log

   Fixing the first error often reveals a second one that was hidden behind it. That's normal and a good sign — you're peeling the onion. Save All, package again, and read up to the first red Error line once more.

   If the message is genuinely cryptic, copy the exact error sentence (not the whole log) and search it. Because Unreal's errors are specific and shared by thousands of developers, a precise search usually lands on the answer fast.

   TipCopy ONE error line, not the whole log, when searching or asking for help. The specific sentence is what gets you an answer; the wall of text just buries it.

The other problem: my package is enormous

Say packaging now succeeds — but the output folder is way bigger than your little game has any right to be. The usual reason is simple: by default Unreal cooks everything your project references, plus anything you told it to include wholesale. If you added the Starter Content or a big marketplace pack and only used two assets from it, the rest can still get dragged along.

Trimming a build is two moves: stop cooking content you don't use, then find the heavy assets you do ship and decide whether they need to be that heavy. Unreal has built-in tools for both — you don't guess, you measure.

Shrink the package

Do these in order. The first move alone often cuts the size dramatically.

1. ✓
   1Don't cook what you don't reference

   Go to Edit → Project Settings → Packaging. By default 'Cook everything in the project content directory' may be on, which ships every asset whether or not your game uses it. Turning it off tells Unreal to cook only what's actually referenced from your maps — a big saving if you have unused content lying around.

   If you do need to force-include specific folders (e.g. assets loaded dynamically that aren't directly referenced), use the 'Additional Asset Directories to Cook' list rather than cooking everything.

   TipAfter changing this, always test the packaged build. If something only loaded at runtime goes missing, add just that folder to 'Additional Asset Directories to Cook' — not the whole project.

2. ✓
   2Delete unused content the honest way

   In the Content Browser, right-click your top-level Content folder and pick a 'Migrate' or use the right-click 'Reference Viewer' to see what links to what. Unreal can also show unused assets: the Content Browser has filters and the 'Size Map' to help you spot orphans.

   Be careful — only delete assets nothing references. Unreal will warn you if something points at an asset you try to delete; read that warning rather than forcing it.

   TipRemoving the Starter Content from a finished project (if you only used it while learning) is one of the easiest size wins. Just make sure nothing in your real level still uses it.

3. ✓
   3Open the Size Map on your level

   Right-click your main level (or any heavy asset) in the Content Browser and choose 'Size Map'. It draws a treemap where each box's area is its disk/memory footprint — the biggest boxes are your biggest costs.

   This instantly shows you whether your size is coming from textures, meshes, audio, or one unexpectedly huge asset. You fix what's actually big, not what you assume is big.

   TipTextures are very often the single largest contributor. A handful of 4K/8K textures can dwarf everything else combined.

4. ✓
   4Run the Asset Audit for the whole project

   Open the Asset Audit window from the Tools menu (under Tools → Audit). It lists every asset with sortable columns including disk size and memory size. Click the size column header to sort biggest-first and you'll see your worst offenders across the entire project in one view.

   Use it to confirm the Size Map's story project-wide: which textures are oversized, which meshes have too many triangles, which sounds are uncompressed.

   TipSort by 'Disk Size' to attack package bloat, and by 'Memory Size' when you're chasing runtime performance instead — they're related but not identical.

5. ✓
   5Right-size and compress the heavy assets

   For oversized textures, open the texture and lower its 'Maximum Texture Size' (a UI element doesn't need a 4K texture) or confirm the compression setting matches its use. Unreal compresses textures by default, but a wrong setting can balloon one.

   For audio, prefer compressed formats and reasonable sample rates for sound effects. For meshes, check whether a high-poly asset really needs all those triangles for how close the player ever gets.

   TipChange one heavy asset, re-check the Size Map, and you'll see the box shrink. Measure-change-measure beats guessing every time.