Kitchen & Dining Sizes
Calculators for the measurements a kitchen and a dining room come down to: the island that fits the kitchen and the stools at it, the table and the cloth on it, and the lights over both.

The island
Find the island that fits your kitchen with room to work and walk around it, then choose stools for its counter.
The table
Size the dining table for the people you seat and the room around it.
Lights over the table and island
Size a chandelier for the table or the room, then space a row of pendants over the island.
On the table
Size a tablecloth for your table and the drop you like, from casual to the floor.
Under the table
Choose a rug that keeps the chairs on it when they're pulled out.
Start with the table
A dining room is planned around its table, so size that first. The dining table size calculator takes the number of people you seat and the size of the room, and finds the standard table that seats them and still leaves room to pull the chairs out. If you already have a table, it works the other way and tells you how many it seats.
Measure the room wall to wall, or to the front of a sideboard or cabinet that stays. The table you pick travels on to the next calculators through the links, so you only measure once.
A tablecloth that fits
A tablecloth looks right when it hangs the same way on every side. The tablecloth size calculator adds the drop you like, casual, everyday, formal or to the floor, to your table and finds the standard size that hangs that far all around, for a rectangular, square, oval or round table.
The light over it

A chandelier over the table is sized from the table, not the room. The chandelier size calculator turns the table's width into the diameter to shop for, the fixture's height from your ceiling, and how far above the tabletop it should hang. For a room without a table, like an entryway or a living room, it uses the room's length and width instead.
Over a kitchen island, a row of pendants usually does the job. The pendant light spacing calculator spaces them evenly along the island, keeps the end ones clear of the edges and gives you the height above the counter, so you can mark the ceiling before the electrician arrives.
Seats at the counter

Counter stools and bar stools differ by a few inches of seat height, and those inches decide whether your knees fit under the top. The bar stool height calculator works from your counter's height to the seat height to look for, tells you how many stools fit along it and how deep the knee space should be.
How these tools work
Each calculator states the rule it uses and the assumptions behind it, right on the page under "How we calculate." The result is a starting point you can adjust to your room.
Everything runs in your browser: the numbers you type stay on your device. Use Copy link to save a result or send it to someone helping you shop.
From the blog

12 Dining Room Ideas, With the Sizes That Make Them Fit
Twelve dining room ideas with the numbers behind them: the table your room fits, a rug for the chairs, the chandelier's size and height, and art and curtains.Read the ideas
11 Kitchen Island Ideas, With the Sizes That Make Them Fit
Eleven kitchen island ideas with the numbers behind them: the aisles around the island, stools and overhangs, and how far apart to hang pendants.Read the ideas