Wallpaper Calculator

About the Wallpaper Calculator

Most calculators work wallpaper out by area: the wall area divided by the area of a roll. It sounds reasonable, and it almost always comes out short.

The reason is that wallpaper is hung in full-height strips, called drops, each cut from the roll. Whatever length is left at the end of a roll after the last full drop is usually too short to use, so it is waste. How many drops a roll yields depends on the wall height and on the pattern repeat — and neither of those shows up in an area calculation at all.

This wallpaper calculator counts the way a decorator does. It works out how long each drop must be, how many whole drops a roll gives, how many strips go around the room, and divides — then adds a spare roll from the same batch.

How to Use the Wallpaper Calculator

Choose metres or feet, and enter the room's length, width and wall height.

Pick the roll size. The standard European roll is 10.05 m × 0.53 m.

Enter the pattern repeat from the roll label — in centimetres or inches — or leave it at 0 for plain or random-match paper.

If a wide opening such as a patio door removes whole strips, enter how many. Ordinary doors and windows usually save no full strips.

Choose how many spare rolls to add.

How the Rolls Are Worked Out

  drop length     =  wall height + 10 cm trimming,
                     rounded up to a whole number of pattern repeats
  drops per roll  =  roll length ÷ drop length, rounded down
  strips          =  room perimeter ÷ roll width, rounded up
  rolls           =  strips ÷ drops per roll, rounded up, + spare

Step-by-Step Example

A 4 × 3 m room, 2.4 m walls, standard rolls, plain paper.

  Drop:           2.4 + 0.1           =  2.50 m
  Drops per roll: 10.05 ÷ 2.50        =  4.02  →  4
  Strips:         14 m ÷ 0.53 m       =  26.4  →  27
  Rolls:          27 ÷ 4              =  6.75  →  7, + 1 spare = 8

Now the same room with a 64 cm pattern repeat:

  Drop:           2.5 m rounded up to whole 0.64 m repeats  =  2.56 m
  Drops per roll: 10.05 ÷ 2.56        =  3.9   →  3
  Rolls:          27 ÷ 3              =  9, + 1 spare = 10

The room did not change. The pattern alone added two rolls.

Why Pattern Repeat Matters So Much

On patterned paper, each strip has to be positioned so the pattern lines up with the strip beside it. That means each drop is cut not just to the wall height but to the next whole pattern repeat. The longer the repeat, the more is wasted per drop, and the more likely it is that the roll no longer fits the last drop.

A small repeat, 10 or 20 centimetres, costs little. A large one, 50 to 64 centimetres, can take a roll from four drops to three — a third more rolls for the same room. Always read the repeat from the label before buying.

Some papers are a half-drop match, where the pattern lines up halfway down alternate strips; these waste slightly more again, which the spare roll helps cover.

Doors and Windows

It is tempting to subtract the area of doors and windows. For wallpaper, it rarely works. The strips above a door and below and above a window are short, but they still have to be cut from a roll, and the offcut from each drop is usually too short for anything else. So an ordinary door or window saves little or nothing.

A very wide opening — a patio door, a large bay — can remove one or two full strips. Enter those as whole strips saved.

The Spare Roll and the Batch Number

Every roll carries a batch number (sometimes called a shade or lot number). Rolls printed in different runs can differ slightly in colour, and a strip from another batch can show as a visible stripe on the wall. Buy all the rolls, plus a spare, from the same batch, and check the labels before you start. The spare covers mistakes and later repairs, when the batch will be long gone.

Before You Hang

Check the rolls. Confirm every roll has the same batch number, and unroll a little of each to check for printing faults before cutting.

Prepare the walls. Walls should be smooth, clean and sound. Fill and sand cracks, and size or prime new plaster so the paste does not soak in too fast and the paper can be slid into position.

Plan where to start. Start from a point where a pattern mismatch will be least visible, often a corner behind a door, and hang the first strip to a plumb line rather than the corner, which is rarely true.

Cut all drops at once. With patterned paper, cutting and numbering several drops in sequence makes matching easier and shows early whether the rolls will stretch as far as planned.

Mind the paste. Paste-the-wall papers are applied dry to a pasted wall, while traditional papers are pasted and left to soak for the time on the label; mixing the methods causes bubbles and shrinkage.

Understanding Your Result

Rolls needed is the total, including spares.

How it is worked out shows the strips, drop length and drops per roll.

Pattern repeat shows how many rolls the repeat added.

Worth knowing covers batch numbers.

When Should You Use This Calculator?

Before buying wallpaper, especially patterned paper.

When comparing papers with different repeats.

For a single feature wall, the same method applies by hand: the wall's width divided by the roll width gives the strips, and the strips divided by the drops per roll shown here gives the rolls.

When checking a decorator's estimate.

Common Mistakes

Calculating by area. Count drops per roll instead.

Ignoring the pattern repeat. It can add a third more rolls.

Subtracting doors and windows. They save little paper.

Mixing batch numbers. Colours can differ.

Skipping the spare roll. It is the only exact match you will get.