diff --git a/CHANGELOG.md b/CHANGELOG.md
index d60b436a695..51f98cd48f0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -33,6 +33,7 @@
 
 ### 💡 Enhancements 💡
 
+- Added `MarshalerSizer` interface to `ptrace`, `plog`, and `pmetric` packages. `NewProtoMarshaler` now returns a `MarshalerSizer` (#5929)
 - Add support to unmarshalls bytes into pmetric.Metrics with `jsoniter` in jsonUnmarshaler(#5433)
 - Add httpprovider to allow loading config files stored in HTTP (#5810)
 - Added `service.telemetry.traces.propagators` configuration to set propagators for collector's internal spans. (#5572)
diff --git a/pdata/plog/encoding.go b/pdata/plog/encoding.go
index 4143190ed0b..69a71c260c4 100644
--- a/pdata/plog/encoding.go
+++ b/pdata/plog/encoding.go
@@ -14,6 +14,12 @@
 
 package plog // import "go.opentelemetry.io/collector/pdata/plog"
 
+// MarshalerSizer is the interface that groups the basic Marshal and Size methods
+type MarshalerSizer interface {
+	Marshaler
+	Sizer
+}
+
 // Marshaler marshals pdata.Logs into bytes.
 type Marshaler interface {
 	// MarshalLogs the given pdata.Logs into bytes.
diff --git a/pdata/plog/pb.go b/pdata/plog/pb.go
index 8c14b0d0385..a12c967edcc 100644
--- a/pdata/plog/pb.go
+++ b/pdata/plog/pb.go
@@ -19,12 +19,12 @@ import (
 	otlplogs "go.opentelemetry.io/collector/pdata/internal/data/protogen/logs/v1"
 )
 
-// NewProtoMarshaler returns a Marshaler. Marshals to OTLP binary protobuf bytes.
-func NewProtoMarshaler() Marshaler {
+// NewProtoMarshaler returns a MarshalerSizer.
+// Marshals to OTLP binary protobuf bytes and calculates the size of the marshaled Logs.
+func NewProtoMarshaler() MarshalerSizer {
 	return newPbMarshaler()
 }
 
-// TODO(#3842): Figure out how we want to represent/return *Sizers.
 type pbMarshaler struct{}
 
 func newPbMarshaler() *pbMarshaler {
diff --git a/pdata/plog/pb_test.go b/pdata/plog/pb_test.go
index c650b7506f5..64dbe7b2bdc 100644
--- a/pdata/plog/pb_test.go
+++ b/pdata/plog/pb_test.go
@@ -31,12 +31,11 @@ func TestProtoLogsUnmarshaler_error(t *testing.T) {
 }
 
 func TestProtoSizer(t *testing.T) {
-	sizer := NewProtoMarshaler().(Sizer)
 	marshaler := NewProtoMarshaler()
 	ld := NewLogs()
 	ld.ResourceLogs().AppendEmpty().ScopeLogs().AppendEmpty().LogRecords().AppendEmpty().SetSeverityText("error")
 
-	size := sizer.LogsSize(ld)
+	size := marshaler.LogsSize(ld)
 
 	bytes, err := marshaler.MarshalLogs(ld)
 	require.NoError(t, err)
diff --git a/pdata/pmetric/encoding.go b/pdata/pmetric/encoding.go
index 5c9f9b31786..51c5acec3a0 100644
--- a/pdata/pmetric/encoding.go
+++ b/pdata/pmetric/encoding.go
@@ -14,6 +14,12 @@
 
 package pmetric // import "go.opentelemetry.io/collector/pdata/pmetric"
 
+// MarshalerSizer is the interface that groups the basic Marshal and Size methods
+type MarshalerSizer interface {
+	Marshaler
+	Sizer
+}
+
 // Marshaler marshals pmetric.Metrics into bytes.
 type Marshaler interface {
 	// MarshalMetrics the given pmetric.Metrics into bytes.
diff --git a/pdata/pmetric/pb.go b/pdata/pmetric/pb.go
index 40fe605080c..db05b35c253 100644
--- a/pdata/pmetric/pb.go
+++ b/pdata/pmetric/pb.go
@@ -19,12 +19,12 @@ import (
 	otlpmetrics "go.opentelemetry.io/collector/pdata/internal/data/protogen/metrics/v1"
 )
 
-// NewProtoMarshaler returns a Marshaler. Marshals to OTLP binary protobuf bytes.
-func NewProtoMarshaler() Marshaler {
+// NewProtoMarshaler returns a MarshalerSizer.
+// Marshals to OTLP binary protobuf bytes and calculates the size of the marshaled Metrics.
+func NewProtoMarshaler() MarshalerSizer {
 	return newPbMarshaler()
 }
 
-// TODO(#3842): Figure out how we want to represent/return *Sizers.
 type pbMarshaler struct{}
 
 func newPbMarshaler() *pbMarshaler {
diff --git a/pdata/pmetric/pb_test.go b/pdata/pmetric/pb_test.go
index b50041e17ce..3be66f16abc 100644
--- a/pdata/pmetric/pb_test.go
+++ b/pdata/pmetric/pb_test.go
@@ -31,12 +31,11 @@ func TestProtoMetricsUnmarshaler_error(t *testing.T) {
 }
 
 func TestProtoSizer(t *testing.T) {
-	sizer := NewProtoMarshaler().(Sizer)
 	marshaler := NewProtoMarshaler()
 	md := NewMetrics()
 	md.ResourceMetrics().AppendEmpty().ScopeMetrics().AppendEmpty().Metrics().AppendEmpty().SetName("foo")
 
-	size := sizer.MetricsSize(md)
+	size := marshaler.MetricsSize(md)
 
 	bytes, err := marshaler.MarshalMetrics(md)
 	require.NoError(t, err)
diff --git a/pdata/ptrace/encoding.go b/pdata/ptrace/encoding.go
index e1c2d72a33d..25fa14e0cdf 100644
--- a/pdata/ptrace/encoding.go
+++ b/pdata/ptrace/encoding.go
@@ -14,6 +14,12 @@
 
 package ptrace // import "go.opentelemetry.io/collector/pdata/ptrace"
 
+// MarshalerSizer is the interface that groups the basic Marshal and Size methods
+type MarshalerSizer interface {
+	Marshaler
+	Sizer
+}
+
 // Marshaler marshals pdata.Traces into bytes.
 type Marshaler interface {
 	// MarshalTraces the given pdata.Traces into bytes.
diff --git a/pdata/ptrace/pb.go b/pdata/ptrace/pb.go
index acc4440d7ce..e164145904a 100644
--- a/pdata/ptrace/pb.go
+++ b/pdata/ptrace/pb.go
@@ -19,12 +19,12 @@ import (
 	otlptrace "go.opentelemetry.io/collector/pdata/internal/data/protogen/trace/v1"
 )
 
-// NewProtoMarshaler returns a Marshaler. Marshals to OTLP binary protobuf bytes.
-func NewProtoMarshaler() Marshaler {
+// NewProtoMarshaler returns a MarshalerSizer.
+// Marshals to OTLP binary protobuf bytes and calculates the size of the marshaled Traces.
+func NewProtoMarshaler() MarshalerSizer {
 	return newPbMarshaler()
 }
 
-// TODO(#3842): Figure out how we want to represent/return *Sizers.
 type pbMarshaler struct{}
 
 func newPbMarshaler() *pbMarshaler {
diff --git a/pdata/ptrace/pb_test.go b/pdata/ptrace/pb_test.go
index 19d85643fca..cb50d5a5f77 100644
--- a/pdata/ptrace/pb_test.go
+++ b/pdata/ptrace/pb_test.go
@@ -31,13 +31,12 @@ func TestProtoTracesUnmarshaler_error(t *testing.T) {
 }
 
 func TestProtoSizer(t *testing.T) {
-	sizer := NewProtoMarshaler().(Sizer)
 	marshaler := NewProtoMarshaler()
 	td := NewTraces()
 	rms := td.ResourceSpans()
 	rms.AppendEmpty().ScopeSpans().AppendEmpty().Spans().AppendEmpty().SetName("foo")
 
-	size := sizer.TracesSize(td)
+	size := marshaler.TracesSize(td)
 
 	bytes, err := marshaler.MarshalTraces(td)
 	require.NoError(t, err)