Three Quarter Inch 3/4″ (21mm) Electrical Conduit Dimensions

Three Quarter Inch 3/4″ is the trade size, not the actual dimension of electrical conduit.  Twenty One 21 is the metric designator not the actual dimension in millimeters.  The  dimensions for various types of 3/4″ electrical conduit are below.  The information was derived from several sources and should not be considered precise.  Dimensions may vary slightly between manufacturers.

3/4 Inch Electrical Conduit Dimensions

3/4″ (21) Electrical Metallic Tubing (EMT or Thinwall) is a smooth light weight galvanized metal conduit that has an inside diameter of .824″ or 20.93mm.  It has an outside diameter of 0.922″ or 23.4mm.  The wall thickness of 3/4″ EMT is .049″ or 1.25mm.  It requires a 1 1/8″″ hole for the conduit fittings.  A tap needs a 59/64″ hole.  Threads per inch for the fittings is 14 NPT.

3/4″ (21) 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.  100′ of 3/4″ RMC weighs approximately 109 pounds or 49.4 kilograms.  It has an inside diameter of 0.824″ or 20.93mm.  It has an outside diameter of 1.050″ or 26.7mm.  The wall thickness is .107″ or 2.70mm.  It requires a 1 1/8″″ hole for the conduit fittings.  A tap needs a 59/64″ hole.  Threads per inch for the fittings is 14 NPT.

3/4″ (21) 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.  It also utilizes the same couplings and fittings as RMC.  3/4″ IMC has an inside diameter of 0.864″ or 21.9mm.  It has an outside diameter of 1.029″ or 26.1mm.  The wall thickness is .083″ or 2.1mm.  It requires a 1 1/8″″ hole for the conduit fittings.  A tap needs a 59/64″ hole.  Threads per inch for the fittings is 14 NPT.

3/4″ (21) Flexible Metal Conduit (FMC or Greenfield) is a galvanized finished flexible metal electrical conduit composed of a continuously formed interlocking metal strip.  3/4″ FMC has a minimum inside diameter of 0.812″ or 20.6248mm and a maximum inside diameter of 0.835″ or 21.209mm.  It has a minimum outside diameter of 1.045″ or 26.543mm and a maximum outside diameter of 1.105″ or 28.067mm.  The minimum bending radius is 5 inches or 101.6mm.  It requires a 1 1/8″″ hole for the conduit fittings.  A tap needs a 59/64″ hole.  Threads per inch for the fittings is 14 NPT.

3/4″ (21) 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 0.824″ or 20.9296mm.  It has an outside diameter of 1.050″ or 26.67mm.  The wall thickness is .113″ or 2.8702mm.  It requires a 1 1/8″″ hole for the conduit fittings.  A tap needs a 59/64″ hole.  Threads per inch for the fittings is 14 NPT.

3/4″ (21) 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 0.742″ or 18.8468mm.  It has an outside diameter of 1.050″ or 26.67mm.  The wall thickness is .154″ or 3.9116mm.  It requires a 1 1/8″″ hole for the conduit fittings.  A tap needs a 59/64″ hole.  Threads per inch for the fittings is 14 NPT.

3/4″ (21) Electrical Nonmetallic Tubing (ENT or Smurf) is a nonmetallic, non-conductive flexible conduit with an inside diameter of .76″ or 19.304mm.  3/4″ ENT has an outside diameter of 1.05″ or 26.67mm.  The minimum bend radius is 6 inches.  It requires a 1 1/8″″ hole for the conduit fittings.  A tap needs a 59/64″ hole.  Threads per inch for the fittings is 14 NPT.

3/4″ (21) 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.  It has an inside minimum diameter of .820″ or 20.828mm and a maximum inside diameter of .840″ or 21.336mm.  It has a minimum outside diameter of 1.030″ or 26.162mm and a maximum outside diameter of 1.050″ or 26.67mm.  The minimum bending radius is 5 inches.  It requires a 1 1/8″″ hole for the conduit fittings.  A tap needs a 59/64″ hole.  Threads per inch for the fittings is 14 NPT.

3/4″ (21) Liguidtight Flexible Nonmetallic Conduit (LFNC) is a nonmetallic conduit that is suitable for wet conditions.  It has an inside minimum diameter of .820″ or 20.828mm and a maximum inside diameter of .840″ or 21.336mm.  It has a minimum outside diameter of 1.030″ or 26.162mm and a maximum outside diameter of 1.050″ or 26.67mm.  The minimum bending radius is 5 inches.  It requires a 1 1/8″″ hole for the conduit fittings.  A tap needs a 59/64″ hole.  Threads per inch for the fittings is 14 NPT.

3/4″ (21) Reinforced Thermosetting Resin Conduit (RTRC) is a nonmetallic conduit that is suitable for many conditions.  It has an inside diameter of .910″ or 23.114mm.  Outside diameter is 1.050″ or 26.67mm..  The conduit wall thickness is .070 or 1.778mm.  100 feet of three quarter inch SW RTRC weighs 17 pounds or 7.711064 kilograms.  It requires a 1 1/8″″ hole for the conduit fittings.  A tap needs a 59/64″ hole.  Threads per inch for the fittings is 14 NPT.

3/4″ (21) 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 1.050″ or 26.67mm.  Type SDR-9 has an inside diameter of .796″ or 20.2184mm.  100 feet of 3/4″ HDPE weighs 15 pounds or 6.80388.  The wall thickness is .117″ or 2.9718mm.

All three quarter 3/4″ (21) conduit and fittings require a inch and one eighth 1 1/8″ opening into an electrical box.  The hole can be made with a hole saw or a knockout punch.

A tap for three quarter 3/4″ (21) conduit or conduit fittings requires a 59/64″ hole.  The threads per inch is 14 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 Conduit Dimensions

1/2″ (16)        1″ (27)         1 1/4″ (35)

1 1/2″ (41)       2″ (53)         2 1/2″ (63)

3″ (78)        3 1/2″ (91)         4″ (103)

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.