Four Inch (103) Electrical Conduit Dimensions

Four Inch 4″ is the trade size, not the actual dimension of electrical conduit.  One hundred and three 103 is the metric designator not the actual dimension in millimeters.  The dimensions for various types of 4″ electrical conduits are below.  The information was derived from several sources and should not be considered precise.  Dimensions may vary slightly between manufacturers.

Four Inch Electrical Conduit Dimensions

4″ (103) Electrical Metallic Tubing (EMT or Thinwall) is a smooth lightweight galvanized metal conduit that has an inside diameter of 4.334″ or 110.08mm.  The outside diameter is 4.500″ or 114.3mm.  The wall thickness of 4″ EMT is .083″ or 2.11mm.  100 feet of 4″ EMT weighs approximately 393 pounds or 178.2 kilograms.  It requires a 4.5″ hole for the conduit fittings.  A tap needs a 4.25″ hole.  Threads per inch for the fittings is 8 NPT.

4″ (103) Rigid Metal Conduit (RMC) is a heavy weight conduit with a galvanized finish throughout.  It has factory threads with a 3/4″ per foot taper, 8 threads per inch NPT.  100′ of 4″ RMC weighs approximately 1030 pounds or 467.1 kilograms.  It has an inside diameter of 4.026″ or 102.26mm  It has an outside diameter of 4.500″ or 114.3mm.  The wall thickness is .225″ or 5.70mm.  4″ Rigid requires a 4.5″ hole for the conduit and fittings.  A tap needs a 4.25″ hole.

4″ (103) Intermediate Metal Conduit (IMC) is a lighter weight version of RMC.  It has a galvanized finish inside and out and can be used in many of the same environments as RMC.  It has factory threads with a 3/4″ per foot taper, and 8 threads per inch NPT.  It also utilizes the same couplings and fittings as RMC.  100 feet of 4″ IMC weighs approximately  700 pounds or 317.5 kilograms.  4″ IMC has an inside diameter of 4.166″ or 1.5.4mm.  It has an outside diameter of 4.466″ or 113.4mm.  The wall thickness is .15″ or 3.81mm.

4″ (103) Flexible Metal Conduit (FMC or Greenfield) is a galvanized finished flexible metal electrical conduit composed of a continuously formed interlocking metal strip.  100 feet of 4″ Reduced Wall Steel Greenfield weighs approximately 270 pounds (122.47 kilograms).  Reduced Wall 4″ Aluminum FMC weighs 76 pounds or 34.47 kilograms.  4″ FMC has a minimum inside diameter of 4.000″ or 101.6mm.  It has a minimum outside diameter of 4.360″ or 110.744mm and a maximum outside diameter of 4.560″ or 115.824mm.  The minimum bending radius is 24 inches or 609.6mm.  4″ Flex requires a 4.5″ hole for the conduit fittings.  A tap needs a 4.25″ hole.  Threads per inch for the fittings is 8 NPT.

4″ (103) Rigid Polyvinyl Chloride Conduit (PVC) schedule 40 is a nonmetallic, non-conductive electrical conduit that is good to use indoors and outdoors, or underground.  It has some flexibility with an inside diameter of 4.026″ or 102.2604mm.  It has an outside diameter of 4.500″ or 114.3mm.  The wall thickness is .237″ or 6.0198mm.  4″ Schedule 40 weighs 232 pounds per 100 feet (105.233344 kilograms).  4″ PVC requires a 4.5″ hole for the conduit fittings.  A tap needs a 4.25″ hole.  Threads per inch for the fittings is 8 NPT.

4″ (103) Rigid Polyvinyl Chloride Conduit (PVC) schedule 80 is a nonmetallic, non-conductive electrical conduit that is good to use indoors and outdoors, or underground.  It has limited flexibility.  Schedule 80 has an inside diameter of 3.826″ or 97.1804mm.  It has an outside diameter of 4.500″ or 114.3mm.  The wall thickness is .337″ or 8.5598mm.  4″ Schedule 80 weighs 308 pounds per 100 feet or 139.71 kilograms.  4″ PVC requires a 4.5″ hole for the conduit fittings.  A tap needs a 4.25″ hole.  Threads per inch for the fittings is 8 NPT.

4″ (103) Liguidtight Flexible Metal Conduit (LFMC or Sealtight) is a flexible metal conduit with a non-metallic, non-conductive outer jacket that makes it suitable for use in wet locations.  100 feet of 4″ Sealtight weighs 349 pounds or 158.303608 kilograms.  It has an inside minimum diameter of 4.000″ or 101.6mm and a maximum inside diameter of 4.040″ or mm.  It has a minimum outside diameter of 4.460″ or 113.284mm and a maximum outside diameter of 4.500″ or 114.3mm.  The minimum bending radius is 24 inches (609.6mm).  Fittings requires a 4.5″ hole.  A tap needs a 4.25″ hole.  Threads per inch for the fittings is 8 NPT.

4″ (103) Reinforced Thermosetting Resin Conduit (RTRC or Fiberglass) is a nonmetallic conduit that is suitable for many conditions.  It has an inside diameter of 4.320″ or 109.728mm.  Outside diameter is 4.460″ or 113.284mm.  The conduit wall thickness is .070″ or 1.778mm.  100 feet of four inch SW RTRC weighs 72 pounds or 32.658624 kilograms.  It requires a 4.5″ hole for the conduit fittings.  A tap needs a 4.25″ hole.  Threads per inch for the fittings is 8 NPT.

4″ (103) High Density Polyethylene (HDPE) is a non-metallic flexible conduit available in long reel lengths to reduce joints and installation time.  It has an outside diameter of 4.500″ or 114.3mm.  Type SDR-9 has an inside diameter of 3.440″ or 87.376mm.  100 feet of 4″ HDPE weighs 272 pounds or 123.377024 kilograms.  The wall thickness is 0.500″ or 12.7mm.

All four inch 4″ (103) conduit and fittings require a four and a half inch 4 1/2″ opening into an electrical box.  The hole can be made with a hole saw or a knockout punch.

A tap for four inch 4″ (103) conduit or conduit fittings requires a 4 1/4″ hole.  The threads per inch is 8 National Pipe Thread (NPT).

The standard length for most conduits is ten feet 10′ or 3.048 meters.  Twenty foot 20′ (6.096 meters) lengths of metal conduit are available, but not always in stock.  PVC conduit is available in ten foot 10′ and in some sizes, twenty foot 20′ lengths.  RTRC mostly comes in twenty foot 20′ lengths.  The flexible conduits come in various length coils and reels depending on the trade size.  Some electrical supply companies will cut flexible conduit to length.

See my post describing various electrical conduit types.

Other Size Electrical Conduits

1/2″ (16)       3/4″ (21)        1″(27)

1 1/4″ (35)       1 1/2″ (41)        2″ (53)

2 1/2″ (63)       3″ (78)        3 1/2″ (91)

5″ (129)       6″ (155)

For more conduit code details and conduit fill see Chapter 9, Tables 1, 4, 5 and 5A.
See the tables in Informative Annex C in the back of the National Electrical Code (NFPA 70) for the allowable number of wires in each size conduit.