diff --git a/synapse/util/caches/__init__.py b/synapse/util/caches/__init__.py
index 4a83c46d9..4adae9668 100644
--- a/synapse/util/caches/__init__.py
+++ b/synapse/util/caches/__init__.py
@@ -16,7 +16,7 @@
 import synapse.metrics
 import os
 
-CACHE_SIZE_FACTOR = float(os.environ.get("SYNAPSE_CACHE_FACTOR", 0.1))
+CACHE_SIZE_FACTOR = float(os.environ.get("SYNAPSE_CACHE_FACTOR", 0.5))
 
 metrics = synapse.metrics.get_metrics_for("synapse.util.caches")