M4 motorway
mile
km
Eastbound exits (B carriageway)
Junction
Westbound exits (A carriageway)
7.3
11.8
Road continues as A4 to Central London
J1[coord 1]
Start of motorway
8.3 8.5
13.4 13.7
North Circular A406 South Circular A205 Chiswick A315
J2
Staines , Hounslow , Brentford A4
12.5 12.8
20.1 20.6
Heston services
Services
Heston services
13.4 13.7
21.5 22.1
Heathrow (Terminals 4 , 5 & Cargo), Hayes , Harrow , Hounslow A312
J3
Heathrow (Terminals 4 , 5 & Cargo), Hayes, Harrow, Hounslow A312
15.2 15.7
24.5 25.2
Heathrow (Terminals 2 & 3 ) (A4) Uxbridge A408
J4a
Heathrow (Terminals 2 & 3 ) (A4) Uxbridge A408
16.8 17.7
27.0 28.5
Heathrow (Terminals 4 , 5 & Cargo) , Gatwick Airport , Watford (M3) , (M23) , (M40) , (M1) M25
J4b[coord 2]
Heathrow (Terminals 4, 5&Cargo), Gatwick, Watford (M3), (M23), (M40), (M1), M25
19.1 19.5
30.7 31.4
Colnbrook , Langley , Slough (East) A4 Eton , Datchet B470
J5
Colnbrook , Langley , Slough (East) A4 , Datchet B470
22.9 23.2
36.8 37.4
Slough (Central) A355 Windsor A322
J6
Slough (Central) A355 Windsor A322
24.7 25.0
39.8 40.3
Slough (West) A4
J7
Slough (West) A4
27.8 28.2
44.7 45.4
High Wycombe , Henley A404(M) Maidenhead A308(M)
J8/9
High Wycombe , Henley A404(M) Maidenhead A308(M)
35.0 35.8
56.4 57.6
Reading (East) , Wokingham , Bracknell A329(M)
J10
Reading (East) , Wokingham , Bracknell A329(M)
40.6 41.2
65.4 66.3
Basingstoke , Reading (Central & South) A33
J11
Basingstoke , Reading (Central & South) A33
43.5 43.8
70.0 70.5
Reading services
Services
Reading services
45.3 45.7
72.9 73.5
Reading (West) , Theale A4
J12
Reading (West) , Theale A4
56.9 57.2
91.5 92.1
Newbury , Oxford A34 Chieveley services (Moto )
J13Services [coord 3]
Newbury , Oxford A34 Chieveley services (Moto )
64.4 64.8
103.7 104.3
Hungerford , Wantage A338
J14
Hungerford , Wantage A338
68.7
110.5
Membury services
Services
Membury services
76.4 77.1
122.9 124.0
Swindon (East) A419 Marlborough A346 Oxford (A420 )
J15
Swindon A419 , Marlborough A346
82.4 82.8
132.6 133.2
Swindon (West), Royal Wootton Bassett , Wroughton , MoD Lyneham , Calne A3102
J16
Swindon (West) , Royal Wootton Bassett , Wroughton , MoD Lyneham , Calne A3102
94.8 95.3
152.5 153.4
Chippenham A350 Cirencester A429
J17
Chippenham A350 Cirencester A429
96.7
155.7
Leigh Delamere services
Services
Leigh Delamere services
104.9 105.6
168.8 170.0
Bath , Stroud A46
J18
Bath , Stroud A46
112.8 113.2
181.5 182.1
Bristol M32
J19
Bristol M32
115.8 116.3
186.3 187.2
The SOUTH WEST , Bristol (West), The MIDLANDS , Gloucester , Bristol Airport , M5
J20Almondsbury Interchange [coord 4]
The SOUTH WEST, Bristol (West) M5(S) The MIDLANDS, Gloucester M5(N)
117.7 189.5
189.5 190.0
No access
J21
Chepstow M48
121.3 121.6
195.2 195.7
Avonmouth M49
J22
Avonmouth M49
121.7 124.1
195.9 199.8
Entry into England
Second Severn Crossing [coord 5]
Entry into Wales
127.0
204.4
No toll plaza
Bridge Toll
Former Toll plaza (closed Dec 2018)
129.2
208.0
Chepstow M48
J23
No access
131.4 132.2
211.4 212.8
Magor , Caldicot A4810 Magor services
J23A Services
Magor , Caldicot A4810 Magor services
134.8 135.6
217.0 218.3
City centre A48 Newport (East) B4237 Monmouth A449 The MIDLANDS (M50 )
J24
City centre A48 Newport (East) B4237 Monmouth A449
137.9
222.0
No access
J25
Caerleon B4596
138.3
222.6
No access
J25A
Newport , Cwmbran A4042
138.8 139.1
223.4 223.8
Brynglas Tunnels
Tunnel
Brynglas Tunnels
139.1 139.5
223.8 224.5
Newport , Cwmbran , Caerleon A4051
J26
Newport A4051
140.8 141,4
226.6 227.6
High Cross B4591
J27
High Cross B4591
142.0 142.9
228.5 230.0
Newport A48 Risca , Brynmawr A467
J28
Newport A48 Risca , Brynmawr A467
143.6
231.1
No access
J29
Cardiff (East and South) A48(M)
146.6 147.3
236.0 237.0
Cardiff (East) A4232 Cardiff Gate services
J30 Services
Cardiff (East) A4232 Cardiff Gate services
151.9 244.5
244.5 246.1
Merthyr Tydfil , Cardiff A470
J32
Cardiff (North), Merthyr Tydfil A470
155.4 156.0
250.1 251.1
Cardiff (West), Barry , Penarth A4232 Cardiff Airport Cardiff West services
J33Services
Cardiff (West), Barry , Penarth A4232 Cardiff Airport Cardiff West services
157.5 158.1
253.5 254.4
Llantrisant , Rhondda A4119 Royal Glamorgan Hospital
J34
Llantrisant , Rhondda A4119 Royal Glamorgan Hospital
163.9 164.4
263.7 264.5
Pen-coed A473
J35
Bridgend , Pen-coed A473
167.5 168.3
269.6 270.8
Bridgend A4061 Maesteg A4063 Princess of Wales Hospital Sarn Park services
J36Services
Bridgend A4061 Maesteg A4063 Princess of Wales Hospital Sarn Park services
172.8 173.5
278.1 279.3
Pyle , Porthcawl A4229
J37
Porthcawl , Pyle A4229
177.0 177.3
284.9 285.3
Port Talbot A48
J38
Port Talbot A48
178.3
286.9
No access (on-ramp only)
J39
No access
179.7 179.9
289.2 289.6
Port Talbot A4107
J40
Port Talbot A4107
180.9 181.3
291.1 291.8
Port Talbot A48
J41
Briton Ferry A48
183.9 184.9
295.9 297.3
Briton Ferry A48 Swansea (South) A483
J42
Swansea (South) A483
184.9 185.7
297.5 298.8
Neath , Merthyr Tydfil A465
J43
Neath , Merthyr Tydfil A465
187.0 187.4
300.9 301.6
Swansea (East) A48
J44
Swansea (East) A48
188.8 189.3
303.9 304.7
Pontardawe , Swansea (North) A4067
J45
Pontardawe , Swansea (North) A4067
190.8 191.4
307.0 308.0
Llangyfelach B4489 Felindre Morriston Hospital
J46
Llangyfelach B4489 Felindre Morriston Hospital
192.4 193.1
309.6 310.7
Swansea (West) A483 Gorseinon A48 Swansea services
J47Services
Swansea (West) A483 Gorseinon A48 Swansea services
196.4 197.1
316.0 317.2
Pontarddulais , Llanelli A4138
J48
Pontarddulais , Llanelli A4138
199.2
320.6
Start of motorway
J49 TerminusServices [coord 6]
Motorway terminates at a roundabout:Carmarthen A48 Ammanford , Llandeilo A483 Pontarddulais A48Pont Abraham services
1.000 mi = 1.609 km; 1.000 km = 0.621 mi