diff --git a/go.mod b/go.mod
index 38b50a111..548337345 100644
--- a/go.mod
+++ b/go.mod
@@ -102,11 +102,11 @@ require (
 	github.com/stretchr/objx v0.2.0 // indirect
 	github.com/tidwall/match v1.1.1 // indirect
 	github.com/tidwall/pretty v1.2.0 // indirect
-	golang.org/x/mod v0.4.2 // indirect
+	golang.org/x/mod v0.6.0-dev.0.20220106191415-9b9b3d81d5e3 // indirect
 	golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a // indirect
 	golang.org/x/text v0.3.8-0.20211004125949-5bd84dd9b33b // indirect
 	golang.org/x/time v0.0.0-20211116232009-f0f3c7e86c11 // indirect
-	golang.org/x/tools v0.1.8-0.20211022200916-316ba0b74098 // indirect
+	golang.org/x/tools v0.1.10 // indirect
 	golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 // indirect
 	google.golang.org/protobuf v1.27.1 // indirect
 	gopkg.in/macaroon.v2 v2.1.0 // indirect
diff --git a/go.sum b/go.sum
index b4357614c..d0033146d 100644
--- a/go.sum
+++ b/go.sum
@@ -614,8 +614,9 @@ golang.org/x/mod v0.1.1-0.20191105210325-c90efee705ee/go.mod h1:QqPTAvyqsEbceGzB
 golang.org/x/mod v0.1.1-0.20191107180719-034126e5016b/go.mod h1:QqPTAvyqsEbceGzBzNggFXnrqF1CaUcvgkdR5Ot7KZg=
 golang.org/x/mod v0.2.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
-golang.org/x/mod v0.4.2 h1:Gz96sIWK3OalVv/I/qNygP42zyoKp3xptRVCWRFEBvo=
 golang.org/x/mod v0.4.2/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
+golang.org/x/mod v0.6.0-dev.0.20220106191415-9b9b3d81d5e3 h1:kQgndtyPBW/JIYERgdxfwMYh3AVStj88WQTlNDi2a+o=
+golang.org/x/mod v0.6.0-dev.0.20220106191415-9b9b3d81d5e3/go.mod h1:3p9vT2HGsQu2K1YbXdKPJLVgG5VJdoTa1poYQBtP1AY=
 golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180906233101-161cd47e91fd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
@@ -819,8 +820,9 @@ golang.org/x/tools v0.0.0-20210106214847-113979e3529a/go.mod h1:emZCQorbCU4vsT4f
 golang.org/x/tools v0.1.1/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
 golang.org/x/tools v0.1.6-0.20210726203631-07bc1bf47fb2/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
 golang.org/x/tools v0.1.7/go.mod h1:LGqMHiF4EqQNHR1JncWGqT5BVaXmza+X+BDGol+dOxo=
-golang.org/x/tools v0.1.8-0.20211022200916-316ba0b74098 h1:YuekqPskqwCCPM79F1X5Dhv4ezTCj+Ki1oNwiafxkA0=
 golang.org/x/tools v0.1.8-0.20211022200916-316ba0b74098/go.mod h1:LGqMHiF4EqQNHR1JncWGqT5BVaXmza+X+BDGol+dOxo=
+golang.org/x/tools v0.1.10 h1:QjFRCZxdOhBJ/UNgnBZLbNV13DlbnK0quyivTnXJM20=
+golang.org/x/tools v0.1.10/go.mod h1:Uh6Zz+xoGYZom868N8YTex3t7RhtHDBrE8Gzo9bV56E=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
diff --git a/internal/caching/impl_ristretto.go b/internal/caching/impl_ristretto.go
index d7e31596b..52452be70 100644
--- a/internal/caching/impl_ristretto.go
+++ b/internal/caching/impl_ristretto.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"reflect"
 	"time"
+	"unsafe"
 
 	"github.com/dgraph-io/ristretto"
 	"github.com/matrix-org/dendrite/roomserver/types"
@@ -29,6 +30,14 @@ func NewRistrettoCache(maxCost CacheSize, enablePrometheus bool) (*Caches, error
 	}, func() float64 {
 		return float64(cache.Metrics.Ratio())
 	})
+	promauto.NewGaugeFunc(prometheus.GaugeOpts{
+		Namespace: "dendrite",
+		Subsystem: "caching_ristretto",
+		Name:      "cost",
+	}, func() float64 {
+		evicted := cache.Metrics.CostEvicted() + cache.Metrics.CostEvicted()
+		return float64(cache.Metrics.CostAdded() - evicted)
+	})
 	return &Caches{
 		RoomVersions: &RistrettoCachePartition[string, gomatrixserverlib.RoomVersion]{
 			cache: cache,
@@ -86,9 +95,13 @@ func (c *RistrettoCachePartition[K, V]) Set(key K, value V) {
 			panic(fmt.Sprintf("invalid use of immutable cache tries to change value of %v from %v to %v", strkey, v, value))
 		}
 	}
-	cost := int64(1)
+	var cost int64
 	if cv, ok := any(value).(costable); ok {
-		cost = int64(cv.CacheCost())
+		cost = cv.CacheCost()
+	} else if cv, ok := any(value).(string); ok {
+		cost = int64(len(cv))
+	} else {
+		cost = int64(unsafe.Sizeof(value))
 	}
 	c.cache.SetWithTTL(strkey, value, cost, c.MaxAge)
 }