Do I take off the doorway or the space under the radiator?

No. The floor runs to the middle of the doorway, where the door bar sits, and under a radiator. Only take off something fixed that the floor will not go under, such as a kitchen island or a hearth.

Measuring for laminate flooring

Measure the room’s length and width at floor level, multiply them for the area, add an allowance for cuts, then divide by the coverage printed on the pack and round up. That gives whole packs, which is what you buy.

Measure the floor

Measure along the skirting, wall to wall, at the widest point in each direction.
Measure the whole floor. Furniture moves; the floor goes under it.
Something fixed that the floor will not go under, such as a kitchen island, a fitted wardrobe or a hearth, is taken off by hand, or the floor around it is entered as separate rectangles.
A bay or an alcove is its own rectangle: measure its width and depth and add it.
At a doorway, measure to the middle of the door opening, where the door bar will sit.
Write the figures in metres with two decimal places: 4.2 m, 3.6 m.

The sum

Floor area = length × width. With several areas, add them.
Area to buy for = floor area × (1 + allowance ÷ 100).
Packs = area to buy for ÷ coverage of one pack, rounded up to a whole pack.
Left over = packs × coverage − area to buy for.

The coverage of one pack is printed on the pack, and it is not the same from one product to the next, or even between board lengths in the same range. BuildBatch starts with 2 m² as a labelled example and asks you to replace it with the figure off your pack.

Worked example

A room 4.2 m × 3.6 m, packs covering 1.84 m², 10% extra for cuts.

Floor area: 4.2 × 3.6 = 15.12 m²
Plus 10%: 15.12 × 1.1 = 16.632 m²
Packs: 16.632 ÷ 1.84 = 9.04, rounded up to 10 packs
Bought: 10 × 1.84 = 18.4 m², about 1.77 m² over

Notice that 9.04 becomes 10. Nine packs would be 16.56 m², about 0.07 m² short of the 16.632 m² to buy for, and a real shortfall, however small, always buys the next pack.

Now the same room with packs covering 2 m²:

Packs: 16.632 ÷ 2 = 8.316, rounded up to 9 packs
Bought: 18 m², about 1.37 m² over

Same room, same allowance, one pack fewer. The pack size decides the count, which is why the figure has to come from the pack in front of you.

Two areas laid together

A hall 4 m × 2 m and a landing 3 m × 2 m, packs of 2 m², 10% extra.

Floor area: 8 + 6 = 14 m²
Plus 10%: 15.4 m²
Packs: 15.4 ÷ 2 = 7.7, rounded up to 8 packs

Worked as two separate jobs it would be 5 packs + 4 packs = 9. BuildBatch adds the areas before rounding, which assumes offcuts from one area can be used in the other. That is true of a hall and landing laid in one go, and less true of two rooms at opposite ends of the house. If the offcuts cannot be shared, work each room out on its own.

What else the floor needs

The packs are the biggest line, not the only one:

Underlay, over the same area, unless the boards have it attached or the floor is glued down.
A damp-proof membrane or moisture barrier on a concrete or ground floor, unless the underlay includes one.
Expansion spacers, and beading or scotia to cover the gap afterwards: about the room’s perimeter less the doorways, 14.8 m in the example room.
A door bar for each doorway where the new floor meets another.
Joining tape for the underlay.

Do it with BuildBatch

Open the Room Refresh Batch with flooring chosen, type the room, enter the pack coverage from your pack, and it lists the packs, the underlay and the rest, each marked Need or Check first.

What this guide does not cover

Sheet vinyl and carpet, which are sold by roll width and need a different sum. Direction of lay and pattern, beyond the allowance you set. Whether the subfloor is flat, dry and sound, whether the floor suits underfloor heating, and levelling compound: the flooring’s instructions decide, so check first. Stairs.