Flooring calculator packs, underlay and trim

How the flooring calculator adds it up

Packs are the floor area plus your wastage, divided by the coverage of one pack, rounded up to a whole pack. Underlay rolls are the floor area over one roll's coverage, rounded up. For scotia or beading, it works out the wall run from your room sizes, takes 0.76m off for each doorway, divides by the length one piece comes in, and rounds up.

Here is the worked example behind the calculator's starting figures: a living room 4.2m by 3.6m with one door, in 8mm laminate sold in packs of 2.22m², laid in straight rows with 10% wastage, over 15m² rolls of underlay, finished with 2.4m scotia. The pack size is taken from a Wickes 8mm laminate: 9 boards of 1285 × 192mm.

• Floor area: 4.2 × 3.6 = 15.12m².
• With 10% wastage: 15.12 × 1.1 = 16.63m².
• Packs: 16.63 ÷ 2.22 = 7.49, so 8 packs. That is 17.76m², about 1.1m² more than the wastage figure.
• Underlay: 15.12 ÷ 15 = 1.01, so 2 rolls. One roll falls short by 0.12m².
• Scotia: the wall run is 2 × (4.2 + 3.6) = 15.6m. Less a 0.76m doorway, 14.84m. 14.84 ÷ 2.4 = 6.2, so 7 lengths.

How much wastage to allow

Allow 10% for planks laid in straight rows and 15% for herringbone or chevron. Karndean's fitting guide for its Korlok click LVT says to add 10%. The timber flooring supplier Havwoods gives the same split as the calculator: 10% for planks and 15% for herringbone on floors under 100m², dropping to 7% and 12% on larger areas. So on a big open floor over 100m², pick the calculator's 7% option. It has no 12% option, so on a large herringbone floor the 15% setting leaves a little spare.

Herringbone packs are small, so the rounding does less to help you. Wickes's herringbone laminate comes 11 blocks to a pack covering 0.87m². For the same 4.2m by 3.6m room at 15%:

• With 15% wastage: 15.12 × 1.15 = 17.39m².
• Packs: 17.39 ÷ 0.87 = 19.99, so 20 packs, which is 17.40m². Only 0.01m² over the wastage figure.
• What that means: compare the straight-lay example, where rounding up to 8 packs gave over a square metre of spare. On herringbone, the 15% is all the margin you have, so do not trim it to save a pack.

Use the coverage on the pack

Always type the m² printed on the pack you are buying, because it changes from range to range even within one shop. Wickes sells one 8mm laminate in packs of 2.22m² and its herringbone laminate in packs of 0.87m². Karndean's Korlok, as Howdens' fitting guide gives it, comes in packs of 3.195m² for planks and 2.742m² for tiles.

If the pack only lists the board size and count, multiply it out: 9 boards of 1.285m by 0.192m is 2.22m². Type that figure into the calculator.

The same living room in Korlok planks at 10% wastage needs 16.63 ÷ 3.195 = 5.2, so 6 packs. That is 19.17m², 2.5m² more than needed, because big packs round up a long way. On a small room it can be worth asking whether the merchant will split a pack or take an unopened one back.

Underlay: rolls and which type

Underlay goes down edge to edge with no overlap, so the calculator uses the floor area with no wastage and rounds up to whole rolls. A common laminate underlay is a 3mm roll 15m long and 1m wide, such as the Elka Duolay roll at JT Dove, covering 15m². Enter your own roll size if yours differs.

Underlay comes in strips, so the last strip in each room is usually cut short. In the example, 1m strips across a 3.6m wide room take four 4.2m runs, which is 16.8m of roll. If the area result is within a few per cent of a whole roll, buy the next one up.

Check the type as well as the size. EGGER says most European makers want 1 to 3mm under laminate. Wickes's wood fibre underlay boards, sold in packs of 10.03m², are marked as not suitable for LVT. Some LVT has an underlay layer already attached to each plank. Read the LVT maker's instructions before you buy any underlay at all.

Scotia, beading and the expansion gap

Laminate, engineered wood and click LVT are floating floors. They have to sit a few millimetres off every wall so they can move, and scotia or beading covers that gap. EGGER says a gap of 8 to 10mm is typical, and to follow the product's own instructions. Karndean's Korlok guide uses 5mm spacers, and asks for more in certain areas.

Scotia is usually sold in 2.4m lengths, like Toolstation's 15 × 15mm laminate scotia. The calculator divides the wall run, less doorways, by the length you set, and rounds up. That assumes offcuts get used on short walls. A room with lots of short runs, such as a chimney breast and alcoves, can need one or two more. If you enter an L-shaped room as two areas, the calculator counts the line where they join as wall on both sides, so take twice that length off the run.

You do not need scotia where you take the skirting off and refit it over the floor, since the skirting hides the gap. The calculator always works out a scotia figure from the room sizes, so ignore it if you are doing that. Doorways need a threshold bar instead, one per door.

Before the flooring goes down

Let the boards settle in the room first. EGGER recommends 48 hours in the room where the floor will go. Karndean's guide says to take Korlok out of its packaging 48 hours before fitting, with the room between 18 and 27°C.

Measure to the widest point of every recess and doorway, and split an L-shaped room into two rectangles, entered as two areas. Wickes's flooring calculator also warns that wood and stone vary between batches, so buy the whole order together.

The subfloor matters more than the board. Karndean asks for no more than 5mm of variation over a 3m span. If the floor is new screed, check it is dry enough before any floor goes on it: the screed calculator covers drying times. For quoting the job, the quote template lists packs, underlay and labour on one page.

• Not included: damp proof membranes, levelling compound, door trimming, stair nosings or adhesive for glue-down floors.
• It does not cover tiles or carpet. Use the tile calculator for tiles and the carpet calculator for carpet, which is sold off a roll by the metre.
• No costs. Board prices swing too much between ranges and merchants to estimate fairly.

Common questions