diff --git a/compound_packet.go b/compound_packet.go
index 9407258..a621c61 100644
--- a/compound_packet.go
+++ b/compound_packet.go
@@ -110,6 +110,15 @@ func (c CompoundPacket) Marshal() ([]byte, error) {
 	return Marshal(p)
 }
 
+// MarshalSize returns the size of the packet once marshaled
+func (c CompoundPacket) MarshalSize() int {
+	l := 0
+	for _, p := range c {
+		l += p.MarshalSize()
+	}
+	return l
+}
+
 // Unmarshal decodes a CompoundPacket from binary.
 func (c *CompoundPacket) Unmarshal(rawData []byte) error {
 	out := make(CompoundPacket, 0)
diff --git a/extended_report.go b/extended_report.go
index 9e39c7b..db7ca41 100644
--- a/extended_report.go
+++ b/extended_report.go
@@ -545,6 +545,11 @@ func (b *UnknownReportBlock) setupBlockHeader() {
 func (b *UnknownReportBlock) unpackBlockHeader() {
 }
 
+// MarshalSize returns the size of the packet once marshaled
+func (x ExtendedReport) MarshalSize() int {
+	return wireSize(x)
+}
+
 // Marshal encodes the ExtendedReport in binary
 func (x ExtendedReport) Marshal() ([]byte, error) {
 	for _, p := range x.Reports {
diff --git a/full_intra_request.go b/full_intra_request.go
index e778e6d..7c67c50 100644
--- a/full_intra_request.go
+++ b/full_intra_request.go
@@ -88,11 +88,12 @@ func (p *FullIntraRequest) Header() Header {
 	return Header{
 		Count:  FormatFIR,
 		Type:   TypePayloadSpecificFeedback,
-		Length: uint16((p.len() / 4) - 1),
+		Length: uint16((p.MarshalSize() / 4) - 1),
 	}
 }
 
-func (p *FullIntraRequest) len() int {
+// MarshalSize returns the size of the packet once marshaled
+func (p *FullIntraRequest) MarshalSize() int {
 	return headerLength + firOffset + len(p.FIR)*8
 }
 
diff --git a/goodbye.go b/goodbye.go
index 7879fb9..bda1785 100644
--- a/goodbye.go
+++ b/goodbye.go
@@ -32,7 +32,7 @@ func (g Goodbye) Marshal() ([]byte, error) {
 	 *       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 	 */
 
-	rawPacket := make([]byte, g.len())
+	rawPacket := make([]byte, g.MarshalSize())
 	packetBody := rawPacket[headerLength:]
 
 	if len(g.Sources) > countMax {
@@ -126,11 +126,12 @@ func (g *Goodbye) Header() Header {
 		Padding: false,
 		Count:   uint8(len(g.Sources)),
 		Type:    TypeGoodbye,
-		Length:  uint16((g.len() / 4) - 1),
+		Length:  uint16((g.MarshalSize() / 4) - 1),
 	}
 }
 
-func (g *Goodbye) len() int {
+// MarshalSize returns the size of the packet once marshaled
+func (g *Goodbye) MarshalSize() int {
 	srcsLength := len(g.Sources) * ssrcLength
 	reasonLength := len(g.Reason) + 1
 
diff --git a/packet.go b/packet.go
index fc937c1..cdb83c0 100644
--- a/packet.go
+++ b/packet.go
@@ -10,6 +10,7 @@ type Packet interface {
 
 	Marshal() ([]byte, error)
 	Unmarshal(rawPacket []byte) error
+	MarshalSize() int
 }
 
 // Unmarshal takes an entire udp datagram (which may consist of multiple RTCP packets) and
diff --git a/picture_loss_indication.go b/picture_loss_indication.go
index 40bd7bc..56a7de2 100644
--- a/picture_loss_indication.go
+++ b/picture_loss_indication.go
@@ -29,7 +29,7 @@ func (p PictureLossIndication) Marshal() ([]byte, error) {
 	 *
 	 * The semantics of this FB message is independent of the payload type.
 	 */
-	rawPacket := make([]byte, p.len())
+	rawPacket := make([]byte, p.MarshalSize())
 	packetBody := rawPacket[headerLength:]
 
 	binary.BigEndian.PutUint32(packetBody, p.SenderSSRC)
@@ -78,7 +78,8 @@ func (p *PictureLossIndication) Header() Header {
 	}
 }
 
-func (p *PictureLossIndication) len() int {
+// MarshalSize returns the size of the packet once marshaled
+func (p *PictureLossIndication) MarshalSize() int {
 	return headerLength + ssrcLength*2
 }
 
diff --git a/rapid_resynchronization_request.go b/rapid_resynchronization_request.go
index 48bbd4a..dc67d49 100644
--- a/rapid_resynchronization_request.go
+++ b/rapid_resynchronization_request.go
@@ -35,7 +35,7 @@ func (p RapidResynchronizationRequest) Marshal() ([]byte, error) {
 	 *
 	 * The semantics of this FB message is independent of the payload type.
 	 */
-	rawPacket := make([]byte, p.len())
+	rawPacket := make([]byte, p.MarshalSize())
 	packetBody := rawPacket[headerLength:]
 
 	binary.BigEndian.PutUint32(packetBody, p.SenderSSRC)
@@ -70,7 +70,8 @@ func (p *RapidResynchronizationRequest) Unmarshal(rawPacket []byte) error {
 	return nil
 }
 
-func (p *RapidResynchronizationRequest) len() int {
+// MarshalSize returns the size of the packet once marshaled
+func (p *RapidResynchronizationRequest) MarshalSize() int {
 	return headerLength + rrrHeaderLength
 }
 
diff --git a/raw_packet.go b/raw_packet.go
index 291ee36..eafb034 100644
--- a/raw_packet.go
+++ b/raw_packet.go
@@ -43,3 +43,8 @@ func (r RawPacket) String() string {
 	out := fmt.Sprintf("RawPacket: %v", ([]byte)(r))
 	return out
 }
+
+// MarshalSize returns the size of the packet once marshaled
+func (r RawPacket) MarshalSize() int {
+	return len(r)
+}
diff --git a/receiver_estimated_maximum_bitrate.go b/receiver_estimated_maximum_bitrate.go
index bd70973..7be57e6 100644
--- a/receiver_estimated_maximum_bitrate.go
+++ b/receiver_estimated_maximum_bitrate.go
@@ -42,9 +42,8 @@ func (p ReceiverEstimatedMaximumBitrate) Marshal() (buf []byte, err error) {
 	return buf, nil
 }
 
-// MarshalSize returns the size of the packet when marshaled.
-// This can be used in conjunction with `MarshalTo` to avoid allocations.
-func (p ReceiverEstimatedMaximumBitrate) MarshalSize() (n int) {
+// MarshalSize returns the size of the packet once marshaled
+func (p ReceiverEstimatedMaximumBitrate) MarshalSize() int {
 	return 20 + 4*len(p.SSRCs)
 }
 
diff --git a/receiver_report.go b/receiver_report.go
index 0e2bb1f..e917702 100644
--- a/receiver_report.go
+++ b/receiver_report.go
@@ -58,7 +58,7 @@ func (r ReceiverReport) Marshal() ([]byte, error) {
 	 *        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 	 */
 
-	rawPacket := make([]byte, r.len())
+	rawPacket := make([]byte, r.MarshalSize())
 	packetBody := rawPacket[headerLength:]
 
 	binary.BigEndian.PutUint32(packetBody, r.SSRC)
@@ -157,7 +157,8 @@ func (r *ReceiverReport) Unmarshal(rawPacket []byte) error {
 	return nil
 }
 
-func (r *ReceiverReport) len() int {
+// MarshalSize returns the size of the packet once marshaled
+func (r *ReceiverReport) MarshalSize() int {
 	repsLength := 0
 	for _, rep := range r.Reports {
 		repsLength += rep.len()
@@ -170,7 +171,7 @@ func (r *ReceiverReport) Header() Header {
 	return Header{
 		Count:  uint8(len(r.Reports)),
 		Type:   TypeReceiverReport,
-		Length: uint16((r.len()/4)-1) + uint16(getPadding(len(r.ProfileExtensions))),
+		Length: uint16((r.MarshalSize()/4)-1) + uint16(getPadding(len(r.ProfileExtensions))),
 	}
 }
 
diff --git a/rfc8888.go b/rfc8888.go
index 9a3e337..544c6e3 100644
--- a/rfc8888.go
+++ b/rfc8888.go
@@ -94,6 +94,11 @@ func (b CCFeedbackReport) DestinationSSRC() []uint32 {
 
 // Len returns the length of the report in bytes
 func (b *CCFeedbackReport) Len() int {
+	return b.MarshalSize()
+}
+
+// MarshalSize returns the size of the packet once marshaled
+func (b *CCFeedbackReport) MarshalSize() int {
 	n := 0
 	for _, block := range b.ReportBlocks {
 		n += block.len()
@@ -107,7 +112,7 @@ func (b *CCFeedbackReport) Header() Header {
 		Padding: false,
 		Count:   FormatCCFB,
 		Type:    TypeTransportSpecificFeedback,
-		Length:  uint16(b.Len()/4 - 1),
+		Length:  uint16(b.MarshalSize()/4 - 1),
 	}
 }
 
diff --git a/sender_report.go b/sender_report.go
index dc5138e..aaee0ee 100644
--- a/sender_report.go
+++ b/sender_report.go
@@ -96,7 +96,7 @@ func (r SenderReport) Marshal() ([]byte, error) {
 	 *        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 	 */
 
-	rawPacket := make([]byte, r.len())
+	rawPacket := make([]byte, r.MarshalSize())
 	packetBody := rawPacket[headerLength:]
 
 	binary.BigEndian.PutUint32(packetBody[srSSRCOffset:], r.SSRC)
@@ -228,7 +228,8 @@ func (r *SenderReport) DestinationSSRC() []uint32 {
 	return out
 }
 
-func (r *SenderReport) len() int {
+// MarshalSize returns the size of the packet once marshaled
+func (r *SenderReport) MarshalSize() int {
 	repsLength := 0
 	for _, rep := range r.Reports {
 		repsLength += rep.len()
@@ -241,7 +242,7 @@ func (r *SenderReport) Header() Header {
 	return Header{
 		Count:  uint8(len(r.Reports)),
 		Type:   TypeSenderReport,
-		Length: uint16((r.len() / 4) - 1),
+		Length: uint16((r.MarshalSize() / 4) - 1),
 	}
 }
 
diff --git a/slice_loss_indication.go b/slice_loss_indication.go
index 73926dd..014fcb7 100644
--- a/slice_loss_indication.go
+++ b/slice_loss_indication.go
@@ -93,7 +93,8 @@ func (p *SliceLossIndication) Unmarshal(rawPacket []byte) error {
 	return nil
 }
 
-func (p *SliceLossIndication) len() int {
+// MarshalSize returns the size of the packet once marshaled
+func (p *SliceLossIndication) MarshalSize() int {
 	return headerLength + sliOffset + (len(p.SLI) * 4)
 }
 
@@ -102,7 +103,7 @@ func (p *SliceLossIndication) Header() Header {
 	return Header{
 		Count:  FormatSLI,
 		Type:   TypeTransportSpecificFeedback,
-		Length: uint16((p.len() / 4) - 1),
+		Length: uint16((p.MarshalSize() / 4) - 1),
 	}
 }
 
diff --git a/source_description.go b/source_description.go
index 28fccdb..fc29d8e 100644
--- a/source_description.go
+++ b/source_description.go
@@ -97,7 +97,7 @@ func (s SourceDescription) Marshal() ([]byte, error) {
 	 *        +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
 	 */
 
-	rawPacket := make([]byte, s.len())
+	rawPacket := make([]byte, s.MarshalSize())
 	packetBody := rawPacket[headerLength:]
 
 	chunkOffset := 0
@@ -169,7 +169,8 @@ func (s *SourceDescription) Unmarshal(rawPacket []byte) error {
 	return nil
 }
 
-func (s *SourceDescription) len() int {
+// MarshalSize returns the size of the packet once marshaled
+func (s *SourceDescription) MarshalSize() int {
 	chunksLength := 0
 	for _, c := range s.Chunks {
 		chunksLength += c.len()
@@ -182,7 +183,7 @@ func (s *SourceDescription) Header() Header {
 	return Header{
 		Count:  uint8(len(s.Chunks)),
 		Type:   TypeSourceDescription,
-		Length: uint16((s.len() / 4) - 1),
+		Length: uint16((s.MarshalSize() / 4) - 1),
 	}
 }
 
@@ -251,7 +252,7 @@ func (s *SourceDescriptionChunk) Unmarshal(rawPacket []byte) error {
 			return err
 		}
 		s.Items = append(s.Items, it)
-		i += it.len()
+		i += it.Len()
 	}
 
 	return errPacketTooShort
@@ -260,7 +261,7 @@ func (s *SourceDescriptionChunk) Unmarshal(rawPacket []byte) error {
 func (s SourceDescriptionChunk) len() int {
 	chunkLen := sdesSourceLen
 	for _, it := range s.Items {
-		chunkLen += it.len()
+		chunkLen += it.Len()
 	}
 	chunkLen += sdesTypeLen // for terminating null octet
 
@@ -280,7 +281,8 @@ type SourceDescriptionItem struct {
 	Text string
 }
 
-func (s SourceDescriptionItem) len() int {
+// Len returns the length of the SourceDescriptionItem when encoded as binary.
+func (s SourceDescriptionItem) Len() int {
 	/*
 	 *   0                   1                   2                   3
 	 *   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
diff --git a/transport_layer_cc.go b/transport_layer_cc.go
index ce2ecaa..55b2162 100644
--- a/transport_layer_cc.go
+++ b/transport_layer_cc.go
@@ -363,13 +363,18 @@ func (t *TransportLayerCC) packetLen() uint16 {
 
 // Len return total bytes with padding
 func (t *TransportLayerCC) Len() uint16 {
+	return uint16(t.MarshalSize())
+}
+
+// MarshalSize returns the size of the packet once marshaled
+func (t *TransportLayerCC) MarshalSize() int {
 	n := t.packetLen()
 	// has padding
 	if n%4 != 0 {
 		n = (n/4 + 1) * 4
 	}
 
-	return n
+	return int(n)
 }
 
 func (t TransportLayerCC) String() string {
@@ -399,7 +404,7 @@ func (t TransportLayerCC) Marshal() ([]byte, error) {
 		return nil, err
 	}
 
-	payload := make([]byte, t.Len()-headerLength)
+	payload := make([]byte, t.MarshalSize()-headerLength)
 	binary.BigEndian.PutUint32(payload, t.SenderSSRC)
 	binary.BigEndian.PutUint32(payload[4:], t.MediaSSRC)
 	binary.BigEndian.PutUint16(payload[baseSequenceNumberOffset:], t.BaseSequenceNumber)
@@ -430,7 +435,7 @@ func (t TransportLayerCC) Marshal() ([]byte, error) {
 	}
 
 	if t.Header.Padding {
-		payload[len(payload)-1] = uint8(t.Len() - t.packetLen())
+		payload[len(payload)-1] = uint8(t.MarshalSize() - int(t.packetLen()))
 	}
 
 	return append(header, payload...), nil
diff --git a/transport_layer_nack.go b/transport_layer_nack.go
index 3d22801..802b915 100644
--- a/transport_layer_nack.go
+++ b/transport_layer_nack.go
@@ -151,7 +151,8 @@ func (p *TransportLayerNack) Unmarshal(rawPacket []byte) error {
 	return nil
 }
 
-func (p *TransportLayerNack) len() int {
+// MarshalSize returns the size of the packet once marshaled
+func (p *TransportLayerNack) MarshalSize() int {
 	return headerLength + nackOffset + (len(p.Nacks) * 4)
 }
 
@@ -160,7 +161,7 @@ func (p *TransportLayerNack) Header() Header {
 	return Header{
 		Count:  FormatTLN,
 		Type:   TypeTransportSpecificFeedback,
-		Length: uint16((p.len() / 4) - 1),
+		Length: uint16((p.MarshalSize() / 4) - 1),
 	}
 }