# Wallpaper calculator

> Wallpaper calculator: rolls to buy from wall width and height, roll size, pattern repeat and trimming, counted as full-height drops per roll.

Phiên bản tương tác: https://www.calcopenly.com/vi/construction/wallpaper-calculator
Chủ đề: Máy tính xây dựng và nhà ở

Wallpaper is bought by the roll but hung in drops, the full-height strips cut from it. Each drop is the wall height plus a trimming allowance, rounded up to whole pattern repeats so the design lines up. Drops across the walls are the total width divided by the roll width, rounded up; each roll gives its length divided by the drop length, rounded down; rolls to buy are drops divided by drops per roll, rounded up.

The default is 14 m of wall, 2.5 m high, papered with 53 cm × 10.05 m rolls and a 53 cm repeat. Each drop is 2.65 m, a roll yields 3, and 27 drops need 9 rolls.

Offcuts shorter than a drop are waste, which is why dividing wall area by roll area undercounts. The default 35 m² of wall divided by 5.33 m² per roll suggests 7 rolls; hanging it takes 9.

## Dữ liệu đầu vào

- **Total width of walls to paper**: Add up the widths of every wall; for a whole room this is the perimeter.
- **Wall height**
- **Roll width**: A standard UK roll is 53 cm × 10.05 m; other makers' sizes vary, so check the label.
- **Roll length**
- **Pattern repeat**: Printed on the label; 0 for plain paper or a random match.
- **Trimming allowance per drop**: About 5 cm at the top and 5 cm at the bottom.

## Kết quả

- Rolls to buy (rolls) — kết quả chính
- Drops (strips) needed
- Drops per roll
- Length of each drop (m)
- Paper hung (m)
- Wall area (m²)

## Công thức

$$
\text{drop} = \left\lceil \frac{h + \text{trim}}{\text{repeat}} \right\rceil \text{repeat},\quad \text{rolls} = \left\lceil \frac{\lceil W / w_{\text{roll}} \rceil}{\lfloor L_{\text{roll}} / \text{drop} \rfloor} \right\rceil
$$

## Ví dụ có lời giải

### 14 m of wall, 2.5 m high, 53 cm repeat

- Total width of walls to paper: 14 m
- Wall height: 2.5 m
- Roll width: 53 cm
- Roll length: 10.05 m
- Pattern repeat: 53 cm
- **Length of each drop: 2.65 m**
- **Drops per roll: 3**
- **Drops (strips) needed: 27**
- **Rolls to buy: 9 rolls**
- Nguồn đối chiếu: Python decimal: ⌈2.6/0.53⌉ × 0.53 = 2.65 m; ⌊10.05/2.65⌋ = 3; ⌈14/0.53⌉ = 27 drops; 27/3 = 9 rolls

### US double rolls, 40 ft of wall, 8 ft high, 21 in repeat

- Total width of walls to paper: 40 ft
- Wall height: 8 ft
- Roll width: 20.5 in
- Roll length: 33 ft
- Pattern repeat: 21 in
- Trimming allowance per drop: 4 in
- **Drops (strips) needed: 24**
- **Drops per roll: 3**
- **Rolls to buy: 8 rolls**
- Nguồn đối chiếu: Python decimal in inches: ⌈100/21⌉ × 21 = 105; ⌊396/105⌋ = 3; ⌈480/20.5⌉ = 24; 24/3 = 8

### Edge: plain paper, wall is exactly 10 roll widths

- Total width of walls to paper: 5.3 m
- Wall height: 2.4 m
- Roll width: 53 cm
- Roll length: 10.05 m
- Pattern repeat: 0 cm
- **Length of each drop: 2.5 m**
- **Drops per roll: 4**
- **Drops (strips) needed: 10**
- **Rolls to buy: 3 rolls**
- Nguồn đối chiếu: Hand calculation: 5.3/0.53 = 10 drops exactly; 10.05/2.5 = 4 drops per roll; 10/4 = 2.5 → 3 rolls

## Câu hỏi

### How many rolls of wallpaper do I need for a room?

Count drops, not square metres. Divide the total wall width by the roll width and round up for the drops; divide the roll length by the drop length and round down for drops per roll; then divide and round up. A 14 m perimeter with 2.5 m walls, 53 cm × 10.05 m rolls and a 53 cm repeat needs 27 drops at 3 per roll, so 9 rolls.

### What size is a standard roll of wallpaper?

In the UK a standard roll is 10.05 m long and 0.53 m wide, about 5.3 m², according to TradeCalculator UK, which also lists 0.70 m wide rolls and other designer sizes. Because sizes vary by maker, enter the width and length printed on your roll's label.

### How does pattern repeat affect how much wallpaper I need?

Each drop is rounded up to a whole number of repeats so every strip starts at the same point in the pattern. On a 2.4 m wall with 10 cm for trimming, plain paper needs 2.5 m drops and a 10.05 m roll gives 4 of them. A 53 cm repeat makes each drop 2.65 m and a roll gives only 3, so 27 drops take 9 rolls instead of 7.

### Should I subtract doors and windows when measuring for wallpaper?

Usually not. Full-height drops are still hung beside a door and short pieces above and below a window, and those offcuts rarely fit elsewhere, so TradeCalculator UK papers the whole perimeter by default. Deduct only wide full-height openings such as patio doors: a 1.8 m opening is about 3 drops of 53 cm paper.

### Why buy wallpaper rolls with the same batch number?

Colour can differ between production runs, so rolls from two batches may not match when hung side by side. Buy every roll you need with the same batch number at once, and add at least one spare roll for repairs and mistakes, as TradeCalculator UK recommends.

### “Wallpaper calculator” chính xác đến mức nào?

Độ chính xác phụ thuộc vào dữ liệu nhập và giả định của phương pháp. Phép tính thập phân dùng 50 chữ số có nghĩa, nhưng ước lượng, phương pháp số và dữ liệu nguồn có thể kém chính xác hơn; làm tròn khi hiển thị không loại bỏ các giới hạn đó. Ví dụ có lời giải đã đối chiếu với nguồn độc lập: 3. Ví dụ, “14 m of wall, 2.5 m high, 53 cm repeat” được kiểm tra bằng Python decimal: ⌈2.6/0.53⌉ × 0.53 = 2.65 m; ⌊10.05/2.65⌋ = 3; ⌈14/0.53⌉ = 27 drops; 27/3 = 9 rolls.

### Phương pháp này lấy từ đâu?

DecoratorsBest — wallpaper estimator with pattern repeat (drops-per-roll method); TradeCalculator UK — wallpaper rolls for 10.05 m × 0.53 m rolls.

## Nguồn

- [DecoratorsBest — wallpaper estimator with pattern repeat (drops-per-roll method)](https://www.decoratorsbest.com/pages/wallpaper-estimator-with-pattern-repeat-for-rolls)
- [TradeCalculator UK — wallpaper rolls for 10.05 m × 0.53 m rolls](https://tradecalculator.co.uk/painting/wallpaper-calculator/)