Inch and a Quarter (35mm) Electrical Conduit Dimensions

Close shot of an inch and one quarter EMT conduit bender
Close shot of an inch and one quarter EMT conduit bender. This bender can also be used to bend one inch rigid metal conduit and 1" aluminum electrical conduit. The marks on the bender are to assist with bending the conduit at different angles when the bending formulas are used.

One Inch and a Quarter 1 1/4″ is the trade size, not the actual dimension of electrical conduit.  Thirty Five 35 is the metric designator not the actual dimension in millimeters.  The dimensions for various types of 1 1/4″ electrical conduits are below.  The information was derived from several sources and should not be considered precise.  Dimensions may vary slightly between manufacturers.

One Inch & One Quarter Conduit Dimensions

1 1/4″ (35) Electrical Metallic Tubing (EMT or Thinwall) is a smooth lightweight galvanized metal conduit that has an inside diameter of 1.380″ or 35.05mm.  The outside diameter is 1.510″ or 38.35mm.  The wall thickness of 1 1/4″ EMT is 0.065″ or 1.65mm.  100 feet of 1 1/4″ EMT weighs approximately 101 pounds or 45.8 kilograms.  It requires a 1 3/4″ hole for the conduit fittings.  A tap needs a 1 1/2″ hole.  Threads per inch for the fittings is 11.5 NPT.

1 1/4″ (35) Rigid Metal Conduit (RMC) is a heavy weight conduit with a galvanized finish throughout.  It has factory threads 11.5 NPT with a 3/4″ per foot taper.  100′ of 1 1/4″ RMC weighs approximately 218 pounds or 98.9 kilograms.  It has an inside diameter of 1.380″ or 35.05mm.  It has an outside diameter of 1.660″ or 42.2mm.  The wall thickness is .133″ or 3.40mm.  1 1/4″ Rigid requires a 1 3/4″ hole for the conduit and fittings.  A tap needs a 1 1/2″ hole.

1 1/4″ (35) 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 11.5 threads per inch NPT.  It also utilizes the same couplings and fittings as RMC.  100 feet of 1 1/4″ IMC weighs approximately 158 pounds or 71.7 kilograms.  1 1/4″ IMC has an inside diameter of 1.468″ or 36.8mm.  It has an outside diameter of 1.638″ or 41.6mm.  The wall thickness is .095″ or 2.41mm.

An inch and one quarter EMT bender standing upright
An inch and one quarter electrical conduit bender standing upright. The bender can also be used for one inch rigid and 1″ aluminum electrical conduit. There are formulas that electricians use to calculate the degree angle and length for elbows, offsets, and saddle bends. The electrical conduit bender has a long handle that is not shown in this photo.

1 1/4″ (35) 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 1 1/4″ Reduced Wall Steel Greenfield weighs approximately 65 pounds (29.48 kilograms).  Reduced Wall 1 1/4″ Aluminum FMC weighs 24 pounds or 10.88 kilograms.  1 1/4″ FMC has a minimum inside diameter of 1.250″ or 31.75mm and a maximum inside diameter of 1.300″ or 33.02mm.  It has a minimum outside diameter of 1.550″ or 39.37mm and a maximum outside diameter of 1.630″ or 41.40mm.  The minimum bending radius is 8 inches or 203.2mm.  1 1/4″ Flex requires a 1 3/4″ hole for the conduit fittings.  A tap needs a 1 1/2″ hole.  Threads per inch for the fittings is 11.5 NPT.

1 1/4″ (35) 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 1.380″ or 35.05mm.  It has an outside diameter of 1.660″ or 42.16mm.  The wall thickness is .140″ or 3.556mm.  1 1/4″ Schedule 40 weighs 46 pounds per 100 feet (20.86 kilograms).  1 1/4″ PVC requires a 1 3/4″ hole for the conduit fittings.  A tap needs a 1 1/2″ hole.  Threads per inch for the fittings is 11.5 NPT.

1 1/4″ (35) 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 1.278″ or 32.46mm.  It has an outside diameter of 1.660″ or 42.16mm.  The wall thickness is .191″ or 4.8514mm.  1 1/4″ Schedule 80 weighs 60 pounds per 100 feet or 27.21 kilograms.  1 1/4″ PVC requires a 1 3/4″” hole for the conduit fittings.  A tap needs a 1 1/2″ hole.  Threads per inch for the fittings is 11.5 NPT.

1 1/4″ (35) Electrical Nonmetallic Tubing (ENT or Smurf) is a nonmetallic, non-conductive flexible conduit with an inside diameter of 1.402″ or 35.61mm.  It weighs 19 pounds per 100 feet or 8.62 kilograms.  1 1/4″ ENT has an outside diameter of 1.660″ or 42.16mm.  The minimum bend radius is 7 inches or 177.8mm.  1 1/4″ fittings requires a 1 3/4″ hole.  A tap needs a 1 1/2″” hole.  Threads per inch for the fittings is 11.5 NPT

1 1/4″ (35) 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 1 1/4″ Sealtight weighs 100 pounds or 45.35 kilograms.  It has an inside minimum diameter of 1.380″ or 35.05mm and a maximum inside diameter of 1.410″ or 35.814mm.  It has a minimum outside diameter of 1.630″ or 41.40mm and a maximum outside diameter of 1.660″ or 42.16mm.  The minimum bending radius is 8 inches (152.4mm).  Fittings requires a 1 3/4″ hole.  A tap needs a 1 1/2″ hole.  Threads per inch for the fittings is 11.5 NPT.

1 1/4″ (35) Liguidtight Flexible Nonmetallic Conduit (LFNC or CarFlex) is a nonmetallic conduit that is suitable for wet conditions.  100′ of 1 1/4″ Carflex weighs 35 pounds or 15.88 kilograms.  It has an inside minimum diameter of 1.380″ or 35.05mm and a maximum inside diameter of 1.410″ or 35.814mm.  It has a minimum outside diameter of 1.630″ or 41.40mm and a maximum outside diameter of 1.660″ or 42.16mm.  The minimum bending radius is 8 inches or 203.2mm.  It requires a 1 3/4″ hole for the conduit fittings.  A tap needs a 1 1/2″ hole.  Threads per inch for the fittings is 11.5 NPT.

1 1/4″ (35) Reinforced Thermosetting Resin Conduit (RTRC or Fiberglass) is a nonmetallic conduit that is suitable for many conditions.  It has an inside diameter of 1.520″ or 38.61mm.  Outside diameter is 1.660″ or 42.16mm..  The conduit wall thickness is .070″ or 1.778mm.  100 feet of one inch and a quarter SW RTRC weighs 23 pounds.  It requires a 1 3/4″ hole for the conduit fittings.  A tap needs a 1 1/2″ hole.  Threads per inch for the fittings is 11.5 NPT.

1 1/4″ (35) 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 1.660″ or 42.16mm.  Type SDR-9 has an inside diameter of 1.270″ or 32.26mm.  100 feet of 1 1/4″ HDPE weighs 37 pounds.  The wall thickness is .184″ or 4.67mm.

All one inch and a quarter 1 1/4″ (35) conduit and fittings require an inch and three quarter 1 3/4″ opening into an electrical box.  The hole can be made with a hole saw or a knockout punch.

A tap for one inch and a quarter 1 1/4″ (35) conduit or conduit fittings requires a 1 1/2″ hole.  The threads per inch is 11.5 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 1/2″ (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.