Why measure
The drain outlet on a disposal has to line up with the trap and the trap arm that leads into the wall. A taller unit can put the outlet lower than the trap arm, and then water has to flow uphill, which does not work. Fixing that may mean changing drain pieces or, in some kitchens, adjusting the drain at the wall.
Width matters too. Sink cabinets in older kitchens can be crowded with water filters, pull-out trash and pipes. Measure before falling in love with a large unit.
Measurements (fill in)
| Measurement | How to take it | Your number |
|---|---|---|
| Sink bottom to center of trap arm in wall | From the underside of the sink to the center of the pipe going into the wall | |
| Sink bottom to cabinet floor | Straight down from the drain opening | |
| Clear width under the drain | Side to side, between obstacles | |
| Distance to outlet | From the drain opening to the outlet | |
| Current unit height | Sink bottom to the bottom of the unit | |
| Current drain outlet height | Sink bottom to center of the side outlet |
Setup details to note
- Plug-in or hardwired.
- Does the current unit have a cord you will reuse, or will the new one need one?
- Wall switch or air switch.
- Dishwasher drains into the disposal: yes or no.
- Single or double sink bowl.
- Sink material: stainless, cast iron, composite or other.
Using the numbers
Check the outlet height
On the new unit's spec sheet, find the distance from the sink to the outlet. It should sit at or above your trap arm.
Check overall height
Make sure the unit clears the cabinet floor and anything stored beneath.
Check width
Compare the unit's diameter with your clear width.
Share with the installer
Send the numbers and photos so they can flag drain changes before the visit.
What a poor fit can add
- Drain pieces
- New elbow, extension or trap
- Wall drain
- Adjusting the trap arm in some cases
- Storage
- Moving filters or pull-outs
- Time
- Extra labor during installation
Common questions
What if the new outlet sits lower than the trap arm?
Ask the installer. Sometimes a different elbow solves it; sometimes a different unit is a better choice.
Does a double sink change anything?
The drain from the other bowl joins the same line, so the layout of the drain pieces matters. Include a photo.
Can I measure with the old unit still installed?
Yes. Measure the current unit and the trap arm, and compare with the new unit's specifications.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.