To measure a wall for wallpaper, take its width at the top, middle and bottom, then its height at the left, center and right. Keep the largest width and the largest height. Record the units, and check the selected wallpaper's trimming instructions before placing the order.

Then check how the wallpaper is sold. A custom mural needs the wall's dimensions and a layout that fits. A roll order needs enough full-height strips, including whatever length the pattern match uses. A square-foot figure alone cannot answer both questions.

Here's how to get from a tape measure to an order you can check.

Measure the area you will actually cover

Use a metal tape measure, a pencil and a simple sketch of the wall. A second person helps keep the tape straight across a wide wall. Clear enough furniture to reach the boundaries rather than measuring around it.

First, choose those boundaries. For a full accent wall, that might be corner to corner and ceiling to the top of the baseboard. If wallpaper will sit above paneling, measure from the top of that paneling to the ceiling. Leave out trim you intend to keep uncovered.

Measure width horizontally and height vertically. Keep the tape taut against the wall; a diagonal or sagging tape gives a different distance.

Take three readings in each direction. For example:

The measured rectangle is 144 inches wide × 96 inches high. Keep the other readings on your sketch, too. They show the installer where the edges vary.

Don't average the readings. An average width of just under 144 inches would leave the widest part short. likewise recommends several measurements and using the largest dimensions.

Walls have a relaxed relationship with right angles. The tape measure is there to settle the matter.

Keep feet, inches and decimal feet straight

Write the unit beside every measurement, even if it seems obvious while you're standing in the room.

12 feet 6 inches = 150 inches = 12.5 feet.

It does not equal 12.6 feet. Decimal feet divide a foot into tenths; feet-and-inches notation divides it into twelve inches. That small typing mistake can change the size of the order.

For a custom order, using inches throughout can make the record easier to check. If a field accepts decimals, 143¾ inches becomes 143.75 inches. Keep your original fraction on the sketch and follow the seller's supported input precision; don't round a measurement down to fit a field.

Howdy's custom-size product configurator offers inches, centimeters and feet. Select the unit first, then check width × height before continuing.

How much wallpaper do you need for a 12-by-8-foot wall?

A wall 12 feet wide and 8 feet high has an area of:

12 × 8 = 96 square feet.

If you measured in inches, the same calculation is:

144 × 96 ÷ 144 = 96 square feet.

The divisor is 144 because a square foot contains 12 × 12 square inches. The final answer is area, so keep “square feet” attached to it.

For a made-to-measure mural, retain 144 inches wide × 96 inches high as the raw wall dimensions. “96 square feet” loses the wall's shape: a narrow, tall wall could have the same area and need a very different crop.

Confirm whether the supplier wants raw wall dimensions or dimensions with a specified allowance added. Keep those two figures separately on your record. This avoids adding an allowance twice or assuming it has already been included.

Measure the full mural wall around a window

A window does more than remove some paper. It interrupts the image.

For a rectangular custom mural that spans the wall, measure the full width and height, including the opening within that rectangle. Wallism's measuring instructions use this approach, with the opening trimmed out during installation. Follow your chosen supplier's layout instructions before ordering.

Suppose the 144 × 96 inch wall has a 36 × 48 inch window. Subtracting the window produces a net area of 84 square feet, but 84 square feet does not describe the mural you need. Keep the full wall rectangle and record:

- The window's outer trim width and height.

- Its distance from the left wall boundary.

- Its distance from the ceiling or other top boundary.

Send a straight-on photo with that sketch. Ask to see where the design's main detail will fall. A mural's focal tree, animal or landscape feature may otherwise land in the opening.

For wallpaper sold in rolls, follow the product's calculator or an installer's strip plan. Don't automatically deduct every opening: pieces above and below it still need usable widths and, for a matched design, the correct pattern position.

Why dividing by roll coverage can leave you short

Wallpaper from a roll usually goes up in vertical strips. Each strip must reach from the top boundary to the bottom, with the specified trimming length. Leftover pieces cannot always be combined into another full strip.

Here is a hypothetical free-match roll example, not a Howdy product size or order recommendation:

The 100-inch cut assumes four inches total for trimming in this example only. Your product's required allowance may differ. Assume no openings, no pattern matching and no loss at the start of a roll.

1. Count strips across the wall: 144 ÷ 21 = 6.86, rounded up to 7 strips.

2. Count complete strips from a roll: 396 ÷ 100 = 3.96, rounded down to 3 strips.

3. Count physical rolls: 7 ÷ 3 = 2.33, rounded up to 3 rolls.

Area division would give a different answer. This roll contains 57.75 square feet, so 96 ÷ 57.75 suggests two rolls. But two rolls yield only six full-height strips under these assumptions. The wall needs seven.

With patterned wallpaper, also check the vertical repeat and match type. A straight match lines up at the same level across neighboring strips; a drop match shifts the pattern between strips. Brewster's specifications explain those differences and why a larger repeat can require more material.

Use the exact product calculator or get the strip plan checked when matching is involved. Confirm usable width, cut length, any seam overlap, reserve material and the purchase unit. A price quoted per single roll may be sold in a double-roll package; check the length of the physical roll you will receive.

Give awkward walls a sketch

For a sloped ceiling, record the widest horizontal span and the tallest vertical span, then draw the slope and its end heights. A rectangular mural may include areas that get trimmed away. Review the crop so the part you want survives that trimming.

Above wainscoting, measure only the intended wallpaper height at several points. For several walls, label each wall and keep its dimensions separately. If you want one mural to continue around a corner, send the wall order and a room sketch for a confirmed panel layout.

A stair wall needs vertical heights and horizontal distances, plus a sketch of the stair line. Avoid using the diagonal along the stairs as the wall height. Wallism's guide illustrates the bounding rectangle for this situation.

What to send Howdy before ordering

Copy this into your notes:

Send the raw dimensions and photo to Howdy's team, with this question:

“My wall measures ___ wide × ___ high in ___. Should I enter these raw dimensions, or add a trimming allowance? Please confirm the order size and how the design will sit around the openings.”

Once that is confirmed, check the selected unit and width/height fields against your notes. Save the confirmed dimensions and layout with the order. That gives you something concrete to refer to when the wallpaper arrives—and gives the installer the same plan you ordered from.