Prep Sink Size: Island and Secondary Sink Dimensions

A second sink sounds like a luxury until you cook with two people in the kitchen. Suddenly one person can rinse vegetables in the island while the other washes pots at the main sink. The catch is that a prep sink has to fit a much tighter footprint, often in a cabinet just 15 to 24 inches wide. The right prep sink size for most islands is a bowl between 12 and 20 inches wide, roughly 16 to 18 inches front to back and 6 to 9 inches deep. A 15 inch square bowl is the most popular all-around choice because it fits an 18 inch cabinet and still holds a colander.

Sizing is about more than the bowl. The sink has to coordinate with cabinet width, the faucet, the drain and supply lines inside the island, the seating overhang and the walking path between the island and the perimeter counters. Plan all of them together so the secondary sink adds work space instead of crowding it.

Typical Prep Sink Size Options

Prep sinks come in a narrow band of widths. These are the common choices and the cabinets they suit.

Prep sink dimensions are usually given as outside width by front to back by depth, for example 15 by 15 by 7 inches. Rectangular models such as 18 by 16 or 22 by 18 offer more room for cutting boards or long produce. Round bowls look nice in a bar area but lose usable corner space, which matters when a sheet pan or baking dish needs a rinse.

How Big Should a Small Prep Sink Be?

The answer depends on what you plan to do there. A small prep sink of 12 to 13 inches is enough for filling a glass, rinsing herbs or washing hands while cooking. It works well as a bar sink beside a beverage fridge. Once you want to drain pasta, wash a head of lettuce or rinse a mixing bowl, step up to 15 inches or more.

Many homeowners regret going too small. If your island and cabinet layout allow it, a 17 or 18 inch bowl gives noticeably more room for very little extra counter space. Interior dimensions are typically 1 to 2 inches smaller than the outside, so a 15 inch sink may have a 13 inch bowl.

Depth for a Prep Sink

• 5 to 6 inches: bar sinks. Fine for glasses but splashes easily.
• 7 to 8 inches: the sweet spot for most prep work. Holds a colander without much splash.
• 9 to 10 inches: best if the prep sink doubles as a second cleanup sink.

Remember that the island cabinet still needs space underneath for the drain trap, and possibly a small disposal. A 9 inch bowl in an 18 inch cabinet with a disposal can get crowded fast.

Cabinet Width and Small Sink Size

Base cabinets come in 3 inch increments. A small sink size has to fit inside the cabinet’s interior, which is narrower than the nominal width because of side panels and face frames. Plan on the sink outside dimension being at least 2 to 3 inches less than the cabinet width.

• 15 inch cabinet: bar sinks up to about 12 inches.
• 18 inch cabinet: 15 inch prep sinks, the most common pairing.
• 21 inch cabinet: 17 to 18 inch sinks.
• 24 inch cabinet: up to about 20 to 21 inches.

An undermount prep sink mounts below the counter, which makes crumbs and scraps easy to sweep into the bowl and looks sleek on stone or quartz. Drop-in models are easier for laminate tops or retrofits.

Island With Small Sink: Layout and Clearances

An island with small sink placement needs to account for traffic, seating and the main work zones. These guidelines come from common kitchen design practice.

Distance From Seating

Keep the sink at least 12 inches, and ideally 18 inches, from the nearest seat. Water splashes, and nobody wants to eat breakfast next to a pile of potato peels. If the sink sits on the working side of the island with seating on the opposite side, make the counter at least 36 to 42 inches deep so the person rinsing and the person sitting each have elbow room, plus 12 to 15 inches of overhang for knees.

Counter on Either Side

Plan for a landing area of at least 18 inches on one side of the sink and about 3 inches on the other. More is better, since prep happens beside the bowl. A sink centered on an island with 24 to 36 inches of counter on each side makes an efficient prep station.

Distance to the Main Sink and Range

The point of a prep sink is to create a second work zone. Place it near the refrigerator and the range so produce goes fridge to sink to cutting board to stove in a short loop. Avoid putting it directly across from the main sink, which turns two cooks into back-to-back collisions.

Aisle Width

Walkways around the island should be at least 42 inches for one cook and 48 inches when two people work at once. A sink in the island makes this more important, because people will stand at it with cabinet doors and dishwasher drawers open nearby.

Faucets and Accessories

A prep sink faucet should be in proportion. A tall pull-down faucet on a 12 inch bowl will splash water over the counter. Look for a spout reach that puts the stream near the center of the bowl and a height that clears a pot but does not tower. Many small sinks come with fitted accessories such as a stainless grid, a cutting board that sits over the bowl, and a colander that rests on ledges. Those extras make a compact sink more useful.

Plumbing Considerations

The plumbing behind an island prep sink is more involved than a wall sink. Islands have no wall for a vent stack, so the drain may need an island vent loop or an approved air admittance valve where local code allows it. Supply lines and the drain usually run through the floor, which means opening the subfloor on a wood frame home or cutting into the slab on a slab foundation.

For these reasons, island prep sinks are a classic job for a licensed plumber. A plumber will size the drain, arrange venting, and pull any permit your jurisdiction requires. If you also want a disposal or an instant hot water dispenser at the prep sink, a licensed electrician will need to add a dedicated outlet or circuit, and kitchen outlets should be GFCI protected.

Steps to Plan a Prep Sink

1. Decide what the sink will do: bar duty, produce prep or full second cleanup. That job sets the prep sink size more than anything else.
2. Choose a bowl width from that use: 12 to 13 inches for bar duty, 15 to 18 inches for prep, 20 inches or more for cleanup.
3. Select the base cabinet width at least 3 inches wider than the sink.
4. Locate the sink on the island with landing space on both sides and at least 12 inches from seating.
5. Confirm aisle widths of 42 to 48 inches.
6. Have a plumber review drain and vent routing before ordering cabinets.
7. Give the actual sink or template to the countertop fabricator before cutting.

Troubleshooting Prep Sink Problems

• Constant splashing: the bowl is too shallow or the faucet is too tall. A deeper bowl, a lower spout, or an aerator with a softer spray helps.
• Slow drain: island drains with poor venting gurgle and drain slowly. A plumber can check the vent arrangement.
• No room under the sink: a narrow cabinet filled with traps, supply valves and a disposal leaves no storage. Consider a slightly wider cabinet or a sink without a disposal.
• Too small to be useful: if you find yourself carrying produce back to the main sink, the bowl is undersized. A 15 inch or larger bowl usually fixes it.

Cost Ranges

Stainless steel prep and bar sinks are typically some of the least expensive sinks you can buy, often under a few hundred dollars, while composite, fireclay and copper versions cost more. Faucets range from budget to premium. The bigger cost is usually installation: running drain, vent and supply lines into an island can add anywhere from several hundred to a few thousand dollars, depending on whether the floor is framed or slab and how far the island is from existing plumbing.

When to Call a Licensed Professional

Adding a sink to an island almost always involves new drain, vent and supply piping, and that work usually requires a permit. Hire a licensed plumber to design and install the plumbing so it meets local code. If the job requires cutting floor joists, check with a contractor or structural professional before cutting, since joists carry load. Any new outlet or circuit for a disposal or hot water dispenser should be installed by a licensed electrician. Before touching existing wiring, turn off the breaker and confirm power is off with a non-contact voltage tester.