Wallpaper Calculator

Estimate wallpaper from full-height strips and usable roll length, rather than wall area alone. Include repeat matching, waste and optional coverage deductions for openings.

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How to Use the Wallpaper Calculator

Choose room length/width or a supplied perimeter. Enter wall height in feet, roll width in inches and roll length in feet. Set pattern repeat in inches and free, straight or half-drop matching. Add openings if you want net coverage area, then set waste and an optional roll price. Enter any additional trimming allowance per strip separately so it does not change reported wall area.

Formula and Explanation

Room strips = 2 × ceil(room length / roll width) + 2 × ceil(room width / roll width)
Perimeter-only strips = ceil(perimeter / roll width)
Straight-match cut = ceil((wall height + trim) / repeat) × repeat
Half-drop cut = straight-match cut + repeat / 2
Strips per roll = floor(roll length / cut length)
Purchase strips = ceil(required strips × (1 + waste / 100))
Rolls = ceil(purchase strips / strips per roll)

All lengths are converted consistently before counting. Free match or zero repeat uses wall height plus the separately entered strip trim. Straight match rounds each cut up to a complete repeat. Half-drop uses an additional half repeat on every cut as a conservative planning allowance, rather than optimizing alternating drops. Room dimensions round each of four walls separately; perimeter-only mode treats the total as one continuous run. Waste is added to strips once, then rolls round up.

Openings reduce the reported wall area only; offcuts above doors or below windows are not assumed to save full-height drops. Roll starts are assumed alignable without extra lead-in loss. Pattern position, trimming, seams, corners, wall irregularities and manufacturer match instructions can require extra material. Half-drop treatment is conservative and not a cutting optimizer. Use the same batch where appropriate and verify the layout before ordering.

Worked Example

A 12 × 10 ft room, 8 ft high, with 24-inch-wide rolls 33 ft long needs 22 full-height strips. Four 8 ft strips fit per roll. With 10% waste, allow 25 strips and buy 7 rolls; at $25 each, cost is $175. A 3 × 7 ft door and 4 × 3 ft window reduce reported coverage from 352 to 319 sq ft, but the full-height strip estimate stays unchanged. With a 20-inch straight repeat, cut length becomes 100 inches and only 3 strips fit each 33 ft roll.

Frequently Asked Questions

Why not divide wall area by roll area?

A roll may have enough total area but insufficient length for another full-height strip. Pattern repeat can further lengthen each cut. This calculator counts strips per roll before rounding roll purchases.

Do windows and doors reduce the roll estimate?

No. They reduce reported coverage area only. Short offcuts may be usable around openings, but that depends on pattern alignment and a real cutting plan; the calculator does not assume those savings.

How is half-drop wallpaper handled?

It adds half a repeat to each repeat-rounded full-height cut. This is a conservative allowance, not an optimized alternating-drop plan. Follow the manufacturer’s match specification and allow for roll-start alignment.

Why can room dimensions differ from a perimeter estimate?

Length/width mode rounds strips separately on four walls so partial strip widths are not shared around corners. Perimeter-only mode treats the entered total as one continuous run, which may need more allowance in an actual room.