Two small floors, one plank. A closet that is 2 and a half feet by 6, and the hallway outside it, 3 and a half by 14. You want the same floor in both, so the question is only how to order it: measure the two, add them up and buy once, or treat them as two jobs and buy twice. The common advice is "add them, you'll save a box." I ran the numbers on six real cartons and the honest answer is that you save a box on two of them. On the other four, the order comes out the same whichever way you count. Whether adding helps is not a property of the advice. It is a property of the carton.
The two floors
The closet is 2.5 × 6 = 15 square feet. The hallway is 3.5 × 14 = 49 square feet. Together that is 64 square feet, and with the 10 percent allowance I use throughout these guides, 64 × 1.10 = 70.4 square feet of plank to buy.
Separately, the same allowance gives 15 × 1.10 = 16.5 for the closet and 49 × 1.10 = 53.9 for the hallway. Note that 16.5 + 53.9 = 70.4. The allowance does not change when you split the job. What changes is how many times you round up.
Six cartons
The six cartons are the ones already on this site, each one a real listing with the coverage printed on the product page. I'll call them by their square footage, because that is the only number that matters for the count:
- 51.33 square feet a carton: a 2 mm glue-down luxury vinyl plank, 7 inches by 48.
- 27.77: a laminate, 9.25 inches wide.
- 23.64: a luxury vinyl plank, 7 by 48.
- 21.24: a laminate, 7.55 inches wide.
- 18.91: a 5 mm rigid-core plank with the pad attached, 7 by 48.
- 18.58: a laminate, 7.55 inches wide.
Cartons = square feet to buy ÷ square feet a carton, rounded up. That rounding is the whole story.
Bought together
70.4 square feet, one division per carton:
- 51.33: 70.4 ÷ 51.33 = 1.37, so 2 cartons.
- 27.77: 70.4 ÷ 27.77 = 2.54, so 3.
- 23.64: 70.4 ÷ 23.64 = 2.98, so 3.
- 21.24: 70.4 ÷ 21.24 = 3.31, so 4.
- 18.91: 70.4 ÷ 18.91 = 3.72, so 4.
- 18.58: 70.4 ÷ 18.58 = 3.79, so 4.
Look at 23.64 for a moment. 2.98 rounds up to 3, but there is almost nothing in hand: 3 cartons is 70.92 square feet against 70.4 to buy, about half a square foot spare after the allowance. Keep that in mind, because it is where the allowance number bites later.
Bought apart
Now two divisions per carton, closet first, then hallway.
The closet at 16.5 square feet is 1 carton for every one of the six. 16.5 is less than 18.58, the smallest carton on the list, so no carton needs a second box. That part is easy.
The hallway at 53.9:
- 51.33: 53.9 ÷ 51.33 = 1.05, so 2 cartons. That .05 is 2.6 square feet over one carton, and it costs a whole second box.
- 27.77: 1.94, so 2.
- 23.64: 2.28, so 3.
- 21.24: 2.54, so 3.
- 18.91: 2.85, so 3.
- 18.58: 2.90, so 3.
Add the closet's 1 to each: 3, 3, 4, 4, 4, 4.
Side by side
| Carton | Together | Apart | Difference |
|---|---|---|---|
| 51.33 | 2 | 1 + 2 = 3 | one box more apart |
| 27.77 | 3 | 1 + 2 = 3 | same |
| 23.64 | 3 | 1 + 3 = 4 | one box more apart |
| 21.24 | 4 | 1 + 3 = 4 | same |
| 18.91 | 4 | 1 + 3 = 4 | same |
| 18.58 | 4 | 1 + 3 = 4 | same |
Two of six. And notice which two. The biggest carton, 51.33, because the hallway alone just barely tips over one box and the closet alone wastes most of a box, and the two half-empty boxes merge into one when you add the areas. And the 23.64 carton, because the combined total sits a hair under 3 boxes while the hallway alone sits a hair over 2, so the closet pushes it to a fourth box only when it is counted on its own.
The other four don't move because their fractions don't line up that way. There is no rule of thumb that tells you which carton you have. You have to do the two divisions and compare.
What the closet wastes on its own
The reason adding ever helps is that a 15-square-foot floor cannot use a whole carton, and the smaller the floor, the larger the fraction of the carton that goes in the garage. Buy one carton for the closet alone and here is what is left over, by carton:
- 51.33: 36.33 square feet left, 242 percent of the floor you laid.
- 27.77: 12.77 left, 85 percent.
- 23.64: 8.64 left, 58 percent.
- 21.24: 6.24 left, 42 percent.
- 18.91: 3.91 left, 26 percent.
- 18.58: 3.58 left, 24 percent.
With the 51.33 carton you buy 3.4 times the closet and leave 2.4 times it on the shelf. That is not a mistake in the arithmetic; it is what a big carton does to a small floor. And it is exactly the paper that the hallway could have used, if the two had been one order.
The allowance barely matters here
I ran the combined 64 square feet at four allowance settings, because the calculator lets you set it and its help text says the number is "Your choice, not an installation recommendation."
| Allowance | 51.33 | 27.77 | 23.64 | 21.24 | 18.91 | 18.58 |
|---|---|---|---|---|---|---|
| 0% | 2 | 3 | 3 | 4 | 4 | 4 |
| 5% | 2 | 3 | 3 | 4 | 4 | 4 |
| 10% | 2 | 3 | 3 | 4 | 4 | 4 |
| 15% | 2 | 3 | 4 | 4 | 4 | 4 |
Zero, five and ten percent give the same six answers. Only at 15 percent does anything move, and only the 23.64 carton, the one with half a square foot to spare at 10 percent. On a floor this small the rounding to whole cartons swallows the allowance whole; the allowance is a few square feet, and a carton is 18 to 51. On the 180-square-foot living room in an earlier guide the same allowance moved the count by one box on two of the three cartons there. Here it is nearly invisible.
So if you were hoping to buy fewer boxes by trimming the allowance from 10 to 5, on this job you will buy exactly the same number. And if you were nervous and set it to 15, you buy one more box on one carton and nothing on the other five.
The calculator does one rectangle, so the adding is yours
The flooring calculator on this site takes a room width and a room length. That is one rectangle. Its help text is explicit: "One rectangle. For an L-shaped room, calculate each rectangle separately and do not overlap them."
Read that sentence again with the table above in mind. Calculating separately is the right way to measure, because a closet and a hallway are not one rectangle and you cannot overlap them. But it is the wrong way to buy, on two of the six cartons, because it rounds twice. The calculator will not add the two areas for you. So do what the help text says for the measuring, then add the two areas on paper and put the total into the calculator once as if it were a single rectangle. There is no field for square feet, only width and length, so give it a rectangle that comes to the same area: 8 by 8 is 64, and so is 16 by 4. The carton count from that one run is the order. The allowance goes on the total, once.
Under every result the calculator prints one more line, and I quote it because it is the boundary of what this guide can tell you: "Purchase quantity only. Allowance is your input, not an installation recommendation. No layout, subfloor, structural or building-code assessment." It counts boxes. It does not know that a hallway plank runs lengthwise or that a closet has a door threshold, and neither does this guide.
The count in one line
Cartons = (area × (1 + allowance)) ÷ carton coverage, rounded up. Two floors in one plank: add the areas first, round once. Then run each floor on its own and compare. If the totals differ, the difference is a real box you don't have to buy.
For the 15 and 49 here: together, 2, 3, 3, 4, 4, 4 cartons across the six sizes; apart, 3, 3, 4, 4, 4, 4. Two cartons save a box. Four don't. The carton on your listing decides which column you're in, so run both before you order.
If you only have time for one of the two, I'd buy together and skip the separate runs. The worst that happens is you buy the same number of boxes you would have bought anyway. Buying apart is the only one of the two that can cost you a carton you didn't need.
Does your closet share a plank with the room outside it?
Sources
Each carton figure was read on the manufacturer's own product page on the date given and is quoted as printed. Every carton count in this article was recomputed with this site's own calculation code on 2026-09-26.
- Shaw Floors, Prime Plank, style 0616V: "Sq. Ft. Per Carton: 51.33", 2 mm glue-down luxury vinyl, planks 7 in by 48 in. https://shawfloors.com/en-us/vinyl/prime-plank-greyed-oak-7-/0616v-00532 (accessed 2026-09-10)
- Shaw Floors, Komondor laminate, style SL123-02216: "Area per Carton 27.77 sq ft", "Width 9.25"". https://shawfloors.com/en-us/laminate/komondor-birchwood-cream/sl123-02216 (accessed 2026-09-24)
- Shaw Floors, Distinction Plus, style 2045V-07066: 23.64 square feet per carton, luxury vinyl planks 7 in by 48 in. https://shawfloors.com/en-us/vinyl/distinction-plus-barrel-oak-7-/2045v-07066 (accessed 2026-09-07)
- Shaw Floors, Oak Grove laminate, style SL119-05066: "Area per Carton 21.24 sq ft", "Width 7.55"". https://shawfloors.com/en-us/laminate/oak-grove-sand-dune-beige/sl119-05066 (accessed 2026-09-24)
- Shaw Floors, Paladin Plus, style 0278V: "Sq. Ft. Per Carton: 18.91", 5 mm rigid core with attached pad, planks 7 in by 48 in. https://shawfloors.com/en-us/vinyl/paladin-plus-fresh-pine-7-/0278v-05052 (accessed 2026-09-10)
- Shaw Floors, Oak Crest laminate, style SL120-05064: "Area per Carton 18.58 sq ft", "Width 7.55"". https://shawfloors.com/en-us/laminate/oak-crest-northwood-gray/sl120-05064 (accessed 2026-09-24)
- Wall Math flooring calculator: the room fields and their help "One rectangle. For an L-shaped room, calculate each rectangle separately and do not overlap them."; the allowance help "Your choice, not an installation recommendation."; and the line printed under every result, "Purchase quantity only. Allowance is your input, not an installation recommendation. No layout, subfloor, structural or building-code assessment." — own site, checked on screen 2026-09-26.
Numbers are a worked example for two small floors. Carton coverage is quoted from the pages above as of the access date; the carton you buy is the source of truth.