Wallpaper Roll Calculator
Rolls needed with pattern repeat.
Special
Half Drop Wallpaper Calculator
Half-drop patterns shift every other strip down by half a repeat, which changes how many drops you get from each roll. See the drops per roll, the waste the offset causes and a strip-by-strip A/B cutting plan.
How it works
- Enter the width of the walls to paper, the wall height and any full-height openings.
- Choose the roll size and enter the pattern repeat; keep the match set to half drop.
- Read the usable drops per roll and the pattern-matching waste.
- Follow the cutting plan: A strips start at the top of a repeat, B strips half a repeat lower.
Formula
Drops = ⌈(wall width − openings) ÷ roll width⌉ A strips start at 0, R, 2R… · B strips start at R/2, 3R/2, 5R/2… Next cut = first position after the previous drop that matches the strip type Rolls = drops cut in order until each roll runs out
R is the pattern repeat. In a half-drop match the design lines up across the seam only if every second strip is shifted down by R/2, so strips alternate between two starting points (A and B). The calculator cuts them in wall order, skipping just enough paper before each cut to reach the right starting point, and reports the paper skipped as pattern-matching waste.
Example
A 16 ft feature wall, 8.5 ft high, with no openings, papered with a half-drop design on a 27 in × 27 ft wide roll with a 25.25 in repeat.
Inputs
- Total width of walls
- 16 ft
- Wall height
- 8.5 ft
- Full-height openings
- 0 ft
- Roll size
- Wide roll (27 in × 27 ft)
- Pattern match
- Half drop
- Pattern repeat
- 25.25 in
- Trim allowance per drop
- 4 in
Result
Rolls to buy4 rolls8 drops of 106 in · half-drop match
Drops needed8
Usable drops per roll2
Pattern-matching waste2.4%
How to recognise a half-drop pattern
Look at the right edge of a strip: in a straight match the motif continues at the same height on the next strip; in a half drop it continues half a repeat lower, so motifs form a diagonal. Manufacturers usually print a symbol on the label — an arrow offset between two bars — and list the repeat, for example “64 cm half drop”.
Half-drop papers often use a little more paper than the same design with a straight match, but the loss depends on the repeat and wall height. Sometimes a half drop wastes less, because the B strips can start partway down the paper left over after an A strip.
Tips for cutting
Number the back of every strip with its A or B type before hanging, and keep the cutting plan beside you. Some installers work from two rolls at once — one for A strips, one for B — which can save a little more than cutting in sequence from one roll.
Frequently asked questions
Does half drop wallpaper need more rolls?
Often, but not always. The offset changes where each strip can start. Depending on the repeat and wall height, a half drop can waste more or less than a straight match; the calculator shows both if you switch the match type.
What is the difference between half drop and straight match?
In a straight match every strip starts at the same point of the pattern. In a half drop every second strip starts half a repeat lower, so the design steps diagonally across the wall.
How do I measure a half-drop repeat?
Use the repeat printed on the label. It is the full vertical repeat of the design; the half drop is half of that value.
Is a cutting plan necessary?
It helps avoid cutting a strip from the wrong point, which is the most common way to run short of half-drop paper.