Coupling sizes follow the nominal pipe size, but the pipe type sets the OD that the coupling must fit. A coupling labeled 4 in is not proof of a fit on every 4-inch cast iron pipe.

Shield width and clamp count are manufacturer catalog values for the named products. For 12 and 15 in, one manufacturer lists 5.50 in wide, 6-clamp couplings. No torque values are shown; use the coupling manufacturer’s instructions.

• Use the coupling manufacturer’s data to confirm the OD range it covers.
• Hubless couplings are for plain-ended pipe. Hub-and-spigot pipe uses compression gaskets sized for Service or Extra Heavy.
• Transition between pipe types needs an adapter or a coupling rated for both.

Weight depends on nominal size, wall, pipe class, product geometry, length and whether a hub is present. Do not calculate commercial weight from nominal wall alone.

Weights are one manufacturer’s approximate values for shipping purposes. Other manufacturers and product lines can differ.

See the Pipe Weight Chart and the Pipe Weight Calculator for other pipe materials.

Pipe lengths

ASTM A74 recognizes 2-1/2, 3-1/2, 5 and 10 ft lengths for Service and Extra Heavy pipe. ASTM A888 covers hubless pipe in 5 ft and 10 ft lengths. Actual availability varies by product and manufacturer.

PVC follows the IPS dimensional system, and cast iron soil pipe has its own. The PVC values are general IPS references; the cast iron values come from the data above. See the PVC Pipe Size Chart and the ABS Pipe Size Chart for plastic DWV pipe.

At some sizes a number can look close, such as Extra Heavy 4-inch at 4.50 in and 4-inch IPS PVC at 4.500 in. A close OD does not make the joints interchangeable: the joint systems differ, and a nominal-size match does not establish coupling compatibility.

Gray cast iron soil pipe is a non-pressure DWV product. Ductile iron pressure pipe is a different material and a different dimensional system.

• Application: soil pipe for gravity drainage; ductile iron for pressurized water and similar service.
• Standards: ASTM A74 and A888 for soil pipe; AWWA standards such as C151/A21.51 for ductile iron.
• Joining and fittings differ, so do not mix them.

A full ductile iron dimensional chart is outside the scope of this page.

Older underground mains may be cast iron pressure pipe with legacy dimensions. Do not treat ASTM A74 soil pipe dimensions as the dimensions of historical cast iron water mains.

• Identify the pipe’s original standard, class and approximate age.
• Measure the actual OD before choosing repair components.
• Use fittings and repair products made for that pipe system.

Gravity drainage depends on slope, loading, venting, fittings and the applicable plumbing code.

For general hydraulics see the Pipe Flow Rate Chart, and for water volume per foot see the Pipe Volume Chart.

Cast iron is heavy, so support and alignment matter at every joint. Use the locally adopted plumbing code and the manufacturer’s instructions for actual requirements.

• Charlotte Pipe’s manual calls for horizontal pipe to be supported at every hub or coupling, with the hanger within 18 in of the joint.
• Where several joints fall within a 4 ft developed length, every other joint can be supported.
• Horizontal pipe and fittings of 5 in and larger must be braced against horizontal movement.
• The manual notes that most plumbing codes require 5 ft pipe to be supported at 5 ft intervals and 10 ft pipe at 10 ft intervals.
• Vertical pipe is secured at each stack base and at intervals that keep the system aligned.

Never test cast iron with compressed air or gas. Manufacturers specify hydrostatic testing to about 10 ft of head (4.3 psi).

For other materials, see the Pipe Support Spacing Chart. Buried pipe also needs correct bedding and corrosion consideration, so follow the manufacturer’s guidance.

ASTM A74-25 covers cast gray iron soil pipe and fittings for gravity-flow plumbing, drain, waste and vent sanitary, and storm water applications.

• Covers Service and Extra Heavy classes.
• Sets requirements for material, manufacture, mechanical and chemical properties, coating, test methods, inspection, certification and markings.
• Includes dimensions and dimensional tolerances for pipe, hubs, spigots and fittings.

The pipe and fittings are not intended for pressure applications.

ASTM A888-24 covers hubless cast iron soil pipe and fittings for use in gravity-flow sanitary, storm drain, waste and vent systems. It establishes requirements for material, manufacture, properties, dimensions, coating, test methods, inspection, certification and product marking.

CISPI 301 is a comparable Cast Iron Soil Pipe Institute specification, and the two are identified together as hubless product specifications. Both are for non-pressure applications.

Do not apply A888 or CISPI 301 dimensions to ASTM A74 Service or Extra Heavy pipe.

Follow this sequence to identify an existing pipe before ordering parts.

1. Identify the joint type: hubless or hub-and-spigot.
2. Measure the plain barrel, not the hub or coupling.
3. Compare the actual OD with the No-Hub, Service and Extra Heavy chart.
4. Inspect markings for size, manufacturer, class and standard.
5. Check the condition: corrosion, coating, ovality and damage.
6. Verify the replacement product against the pipe and coupling manufacturer’s requirements.