How to size a garbage disposal (horsepower isn't everything)
Everyone shops on horsepower. The number that actually sinks installations is cabinet height — and it's the one buried at the bottom of the spec sheet.
We get called out to finish DIY installs fairly often, and the reason is almost never that someone bought too little power. It's that they bought a unit two inches taller than the space under their sink, discovered it at hour two on a Saturday, and now the water's off and the box is open and it can't go back.
So let's do this in the order that actually matters.
1. Measure the cabinet first
Before you look at a single product page: open the cabinet, and measure from the underside of the sink basin straight down to the cabinet floor. Then note what else is under there — a water filter, an RO tank, a pull-out bin, the P-trap for the second basin.
Compare that to the new unit's overall height, and leave yourself an inch of working room. Premium 1 HP units with heavy sound insulation are physically big; that insulation has to go somewhere. This is the single most common reason a replacement goes wrong, and it takes ninety seconds to avoid.
If the new unit's discharge outlet sits at a different height than the old one, your existing P-trap may not line up. It's a two-dollar tailpiece extension and a normal part of the job — but know it before you start, not after.
2. Then pick horsepower — by household, not by ambition
| Motor | Right for | Honest assessment |
|---|---|---|
| 1/2 HP | 1–2 people, light cooking, apartments and rentals | Genuinely enough for coffee grounds and vegetable trimmings. Loud, jams more easily, and it will not deal with bones. Cheapest to buy and to replace. |
| 3/4 HP | 3–5 people who cook most nights | The sweet spot for most families. Noticeably quieter, meaningfully harder to jam, and usually the point at which you start getting a stainless chamber and a real warranty. |
| 1 HP | Large households, heavy cooking, anyone who wants quiet | You're mostly buying quiet and peace of mind, not raw grinding need. Multi-stage grinding handles fibrous waste that stalls smaller units. Tall and expensive. |
| 1 1/4 HP+ | Rarely justified residentially | Diminishing returns in a home kitchen. Spend the difference on sound insulation instead. |
The thing nobody tells you: past 3/4 HP, additional horsepower mostly buys you speed and margin, not capability. What actually separates a pleasant disposal from an unpleasant one is the sound package and the number of grind stages — and those correlate with horsepower only because manufacturers bundle them together at the top of the range.
3. Continuous feed or batch feed?
Continuous feed is what most people have: a wall switch, open drain, feed food in as it runs. Cheaper, more convenient, more choice.
Batch feed only runs when a magnetic stopper is seated in the drain opening. No wall switch, and physically nothing can start while a hand is inside. They cost more and hold less at a time, and they are the right answer in a house with small children. They're also useful if you have no wall switch and don't want to pay an electrician to add one.
4. Check the mounting system before you check out
If the new disposal uses the same mounting system as the old one, the flange stays in the sink and the job drops from ninety minutes to about twenty. InSinkErator uses its own 3-bolt mount; Waste King, Moen and most others use an EZ-mount style collar. Staying within the same family is the cheapest upgrade you'll ever make to your Saturday.
5. The specs that quietly matter
- Grind chamber material. Stainless resists corrosion; galvanised steel on budget units eventually rusts.
- Sound insulation. Marketing names vary. If it's not mentioned at all, there isn't any.
- Grind stages. Two or three stages handle fibrous and stringy waste that stalls a single-stage unit.
- Warranty length. The most honest single signal of how long the manufacturer expects it to last. Two years and lifetime limited are very different statements.
- Power cord. Most units ship without one. Budget another $15 for a cord kit, or plan a hardwired connection.
The short version
Measure the cabinet. Buy 3/4 HP unless you have a reason not to. Stay in the same mounting family as your old unit. Spend your extra money on sound insulation rather than horsepower. And don't open the box until you've checked the height.
The units we install most, sorted by size, budget and noise, are on the shop page — with the cabinet-relevant specs listed on each card.