Is IKEA LILLABO compatible with BRIO? Large curves yes, short ones no
Mostly, and it is the best-measured answer on this site, because somebody put callipers on LILLABO track and published the numbers in an OpenSCAD generator. The large curves fit. The pegs jam. The short curves look like BRIO’s short curves and are nothing of the kind, and that single piece is behind most of the loops that refuse to close.
The large curve: a 3 mm difference
IKEA’s large curve turns 45 degrees on an inner radius of 185 mm, against BRIO’s 182 mm. Eight to a circle, the same as BRIO. Three millimetres on the radius is inside what a run of joints absorbs, so an IKEA large curve stands in for a BRIO one and a mixed circle still closes. This is the only third-party curve anywhere with a measured radius behind it.
The short curve: not a tighter turn
IKEA also makes a curve on a 180 mm inner radius that turns 22.5 degrees — half the angle, on practically the same radius. BRIO’s short curve E1 is the opposite idea: the same 45 degrees on a much tighter 110 mm radius. So they are not substitutes, and they do not behave alike. Drop one IKEA short curve into a loop of large ones and the line comes back 22.5 degrees out, which no amount of joint play will take. Two of them make one large curve’s worth of turn. Use them in pairs, always.
The pegs: 11 mm against 12 mm
The LILLABO peg sits on an 11 mm neck and BRIO’s on a 12 mm one. That one millimetre is the documented reason the two jam: the joint goes together stiffly, sometimes too stiffly to work, and comes apart worse. It does not stop a layout being built, but it is why a child can join BRIO to BRIO and needs help joining BRIO to IKEA.
The straights do not line up
BRIO’s straights are all multiples of 18 mm: 54, 72, 108, 144 and 216. IKEA’s are 50, 100, 146, 205 and 240. They are near-misses rather than matches, and swapping one for the other shifts the line by the difference.
| IKEA straight | Nearest BRIO straight | Difference | Swap it? |
|---|---|---|---|
| 146 mm | 144 mm, medium A | 2 mm | Yes. One joint absorbs it. |
| 50 mm | 54 mm, mini A2 | 4 mm | At a pinch, and not twice in one run. |
| 100 mm | 108 mm, short A1 | 8 mm | No. Not within a joint’s play. |
| 205 mm | 216 mm, long D | 11 mm | No. |
| 240 mm | 216 mm, long D | 24 mm | No. It is longer than anything BRIO makes. |
The useful consequence: in a layout where the straights only have to run from A to B, use whatever you have. In a loop, where the straights on one side have to equal the straights on the other, keep each side to one brand.
The Y pieces are not points
IKEA’s branching pieces are fixed three-way junctions with no moving blade. A BRIO switch has a lever and sends the train the way you set it; an IKEA Y sends it whichever way its wheels happen to find. Worth knowing before you build a layout that depends on a train taking the siding.
Where these numbers come from
IKEA publishes no piece dimensions at all — the product pages and the LILLABO instruction sheet give only the size of the box. Every figure above comes from a published track generator whose author states the constants were taken from original tracks measured, and whose one independently checkable claim, the 11 mm peg neck, matches what everyone else reports. It is a single source, carefully made, and not re-measured here. The whole brand sheet says what is known about the rest.