Auger cable size chart: choosing diameter and length by pipe size

01 /What size auger cable do I need for my pipe?

The right auger cable is the heaviest cable that will still turn every bend between your access point and the clog. That usually means a cable diameter of roughly one-sixth to one-eighth of the pipe diameter for small drains, rising toward one-fifth for main lines where stiffness matters more than flexibility. The chart below shows the typical pairings drain cleaners use.

02 /Why does cable diameter matter so much?

Cable diameter matters because it controls three things at once: how much torque reaches the head, how easily the cable bends, and how much room the cable has to coil inside the pipe. Get the balance wrong and the cable either does not reach the clog with any force or cannot get there at all.

A common mistake is feeding a 1/4-inch hand-drum cable down a basement floor drain into a 3 or 4-inch building drain. It will spin and feel like it is doing something, but in a pipe sixteen times its cross-section it simply lies in a coil. The fix is the next size up, not more effort. The reverse mistake is forcing a 1/2-inch cable through a 1-1/2-inch kitchen trap; take the trap off and enter the trap arm directly instead, as shown in how to snake a sink. If the cable will not advance at all, why a drain snake is not working covers the other causes.

03 /How much cable length do you need?

You need enough cable to reach from the access point to the clog plus roughly 25 percent extra for bends, vertical drops and slack in the drum or feed. Distances inside a house are almost always longer than they look because drains run along joists and around foundations rather than in straight lines.

1. Start at the access point

   Measure from the cleanout or fixture opening along the likely pipe route, not in a straight line.

2. Add vertical drops

   A stack from an upstairs bathroom to the basement is typically 3 to 6 m on its own.

3. Estimate the lateral

   In Canada the building sewer often runs from the front foundation wall to the main under the street. Pace from the wall to the property line and to the centre of the road for a rough figure.

4. Add 25 percent

   Bends and slack consume cable. A lateral that measures 15 m on the ground can need 20 m or more of cable.

5. Check the counter

   Some drum machines have a footage counter. On others, mark the cable with tape every 5 or 10 feet so you can record where the head met resistance.

Recording the distance where the cable stopped is valuable. If a camera inspection is needed later, the contractor can go straight to that point. A clog that stops the cable at the same distance on repeat visits usually sits at a defect, not a random plug; see why the clog came back.

04 /How do you tell what size your pipe is?

The quickest way to tell pipe size is to measure the outside circumference or outside diameter and compare it with the nominal size. Plastic drain pipe (ABS in most of Canada, PVC in some regions) and cast iron are sold by nominal size, and the outside diameter is always larger than the number on the label.

• Cleanout plugs are sized to the pipe they serve; a 4-inch cleanout usually has a plug roughly 3-1/2 inches across.
• Traps often have the size moulded into the plastic or stamped on the slip nut.
• Cast iron has thicker walls, so its outside diameter differs slightly; measure and pick the closest nominal size.

Plastic drain pipe in Canadian homes is typically made to CSA standards; the pipe marking printed along the side usually states the size and material.

05 /Hollow-core or inner-core cable: which should you use?

Use hollow-core cable where flexibility matters most, and inner-core cable where you need to push hard and resist kinking. Hollow-core cable is a coil of wound steel with nothing inside. It bends through tight traps easily and is common on 1/4 and 5/16-inch hand tools. Inner-core cable has a smaller wire coil or strand inside the outer wind, which stiffens it, carries more torque and resists stretching open when the head binds.

• Sinks and tubs: hollow-core 1/4 inch, for the tight trap bends.
• Branches and floor drains: inner-core 3/8 inch if the path has long straight runs; hollow-core if it has many bends.
• Main lines: inner-core drum cable or sectional cable, which is inherently heavier.

06 /How does cable size change for toilets, floor drains and mains?

Each access point has its own sizing quirk. Toilets need a closet auger, not a drum cable, because the trapway is shaped inside the porcelain; see how to auger a toilet, and for reach, what size toilet auger you need. Floor drains often have a trap that is too tight for heavy cable, so the better route is a nearby cleanout; see how to auger a floor drain. Main lines need heavy cable and the right cleanout; see clearing a main line from the cleanout.

If you are unsure where the clog is, size comes second. Use the Clog Locator to find the likely location first, then pick the cable from the chart above. The Auger Cable Sizer applies this chart to one line at a time and adds a starting head, a machine class and a flag when the job belongs to a professional. For the machine that carries each cable, see types of drain augers. And if the chart says you need 7/8-inch sectional cable, that is a strong hint to request quotes rather than rent.

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