Calculate how many rolls of wallpaper you need from your room or wall size, roll size and pattern repeat, or check whether the rolls you have are enough.
Wallpaper Rolls Formula
S = ceil(W / RW)
L = ceil((H + T) / PR) * PR
Rolls = ceil(S / floor(RL / L))
- S is the number of strips (drops) of wallpaper needed
- W is the total width of the walls being papered (ft or m)
- RW is the roll width converted to the same unit as W
- L is the cut length of each strip (ft or m)
- H is the wall height (ft or m)
- T is the combined top and bottom trim allowance, default 4 in (10.16 cm)
- PR is the pattern repeat length converted to the same unit as H and T; skip the rounding step when the paper has no repeat
- RL is the roll length (ft or m)
The calculator makes a whole-strip planning estimate from combined wall width and one uniform height; an installer may need extra strips at individual wall boundaries. It divides the total wall width by the roll width to find how many strips you must hang, works out the cut length of each strip after adding a trim allowance and rounding up to the pattern repeat, then counts how many whole strips one roll yields. Dividing strips needed by strips per roll and rounding up gives the roll count. For a half-drop match, this model conservatively adds half a repeat to every rounded cut. This is a planning allowance, not an optimized alternating-strip cutting plan; starting motif alignment may require additional paper. The second mode reverses the question: enter the rolls you already own and the calculator reports whether they yield enough strips for the room, and if not, how many more rolls to buy. Advanced options let you deduct standard door and window widths, add a waste percentage, and estimate total cost from a price per roll.
Roll Sizes and Strips Per Roll
Wallpaper is sold in a few standard sizes, and the label size determines everything in the math. Roll dimensions and sales units vary by product. The listed sizes are examples; confirm the physical roll dimensions and price unit printed on your label.
| Roll type | Width x length | Total area | Typical usable area |
|---|---|---|---|
| US single roll | 27 in x 13.5 ft | 30.4 sq ft | about 25 sq ft |
| US double roll | 27 in x 27 ft | 60.8 sq ft | about 50 sq ft |
| Standard metric roll | 0.53 m x 10.05 m (20.9 in x 33 ft) | 57.4 sq ft | about 48 sq ft |
| Commercial width | 54 in, sold by the linear yard | varies | varies |
The table below is the part most estimates miss: whole strips per roll by cut length. A roll only yields complete strips, so a small change in cut length, often caused by a pattern repeat, can cross a threshold and drop a whole strip from every roll. That is why a 24 in repeat can push a 7 roll job to 10 rolls while a 36 in repeat on the same wall changes nothing.
| Cut length per strip | US single (13.5 ft) | US double (27 ft) | Metric (10.05 m / 32.97 ft) |
|---|---|---|---|
| 8 ft | 1 strip | 3 strips | 4 strips |
| 8.5 to 9 ft | 1 strip | 3 strips | 3 strips |
| 9.5 to 11 ft | 1 strip | 2 strips | 3 below 10.99 ft; 2 at 11 ft |
| 12 to 13.5 ft | 1 strip | 2 strips | 2 strips |
Example Problems
Example 1: A 12 ft by 10 ft room has 8 ft walls, and the wallpaper is a plain paper with no repeat sold in US double rolls (27 in x 27 ft). The total wall width is 2 * (12 + 10) = 44 ft. Strips needed: ceil(44 / 2.25) = 20. Cut length: 8 ft + 4 in trim = 8.33 ft. Strips per roll: floor(27 / 8.33) = 3. Rolls: ceil(20 / 3) = 7 rolls.
Example 2: The same room uses a paper with a 25.5 in half-drop repeat. The cut length rounds up to the repeat: ceil(8.33 / 2.125) * 2.125 = 8.5 ft, plus half a repeat (1.06 ft) for the drop match, giving 9.56 ft per strip. Strips per roll: floor(27 / 9.56) = 2. Rolls: ceil(20 / 2) = 10 rolls. The pattern repeat turned a 7 roll job into a 10 roll job on identical walls.
FAQ
Supplier guidance: Brewster hanging instructions call for matching batch and pattern numbers and sufficient rolls for the design repeat. Ethan Allen measuring guidance notes that larger straight/drop repeats may require extra rolls. These support product-specific planning; the half-drop arithmetic here is an explicit allowance.
Should you subtract doors and windows from the measurement? Usually no. You still hang full strips above and below openings, and cutting around them creates offcuts you can rarely reuse elsewhere because the pattern must keep matching. Only deduct for very large openings such as patio doors, wide archways, or a wall of windows. The calculator leaves openings out unless you enter them in the advanced options, and even then it only trims one standard width per opening.
What is the difference between a straight match and a half-drop match? With a straight match, the design lines up horizontally, so every strip starts at the same point in the pattern and you only lose the rounding up to the repeat. With a half-drop match, alternating strips are offset by half the repeat, so cutting and starting alignment can need more paper. Actual waste depends on the repeat, wall height and cutting plan. The match type and repeat length are printed on the wallpaper label, often with symbols: arrows aligned for straight match, arrows offset for half-drop.
Why buy an extra roll if the calculator says you have enough? Wallpaper is printed in batches, and the batch or dye lot number on the label changes between print runs. A replacement roll bought months later will often be a slightly different shade, which is visible on a wall even when the pattern matches. One spare roll from the original batch covers hanging mistakes, seam repairs, and future damage. If you end up with leftover full rolls that are unopened, return eligibility depends on the retailer and product. The calculator lists one spare separately from the required-roll quantity and its cost.
