20mm or 30mm quartz worktop: which thickness should you choose?
Thirty millimetre reads more solid and carries a longer unsupported overhang, which matters on a breakfast bar. Twenty millimetre looks lighter and more contemporary, and a mitred edge can make it appear any thickness you want. With us the price band is the same either way.
| 20mm | 30mm | |
|---|---|---|
| Look | Lighter, contemporary | Solid, traditional weight |
| Unsupported overhang | Around 250mm | Around 300mm |
| Weight | Lighter, easier on older units | Heavier, wants sound cabinets |
| Mitred edge | Very common, to fake any thickness | Less often needed |
| Our price band | Same | Same |
The overhang question, which is the one that actually decides it
If you are putting stools under an island, this is the number that matters. A 20mm slab can generally cantilever around 250mm without support, a 30mm slab around 300mm. Go beyond that and you need brackets or a corbel, which is not a disaster but does need planning before the cabinets go in rather than after.
If your island overhang is 300mm or more, tell us at template stage. We would rather design the support in than have you discover it when the stool does not fit.
Mitred edges, and why thickness is partly a choice
A mitred edge is where two pieces are cut at 45 degrees and joined so the stone appears to be a solid block. It means a 20mm slab can present a 60mm, 100mm or even 200mm edge. That is how the chunky waterfall islands you have seen are made, and it is why slab thickness and apparent thickness are two different decisions.
Sinks, and the bit that catches people out
Undermount sinks change the conversation. On 30mm the stone edge around the sink opening is thick enough to be polished into a proper reveal, which looks deliberate. On 20mm that reveal is slimmer, so a lot of kitchens mitre a strip on to build the apparent thickness back up around the sink and the island. Neither is wrong, but it is worth deciding before templating rather than after, because it changes how the piece is cut.
Butler and belfast sinks bring their own detail, since the worktop has to land neatly on the sink rim rather than over it, and that junction is much easier to get right when we have seen the actual sink. Have it on site for the template if you possibly can.
Support, brackets and what your cabinets can take
Stone is heavy. A 30mm quartz worktop weighs roughly half as much again as a 20mm one over the same area, and while a modern rigid carcass takes that without complaint, older units, particularly flat-pack ones that have been moved, sometimes want packing or reinforcing first. We check that at template.
For overhangs beyond the unsupported figures above, the usual answers are steel flat bar let into the cabinet top, or corbels if you want them visible. Both need deciding before the units are finished. It is a five minute conversation at survey and an expensive one afterwards.
Which we would specify
For a straightforward run against a wall, either, and we would let the look decide. For a shaker or classic kitchen, 30mm sits more comfortably. For a handleless contemporary kitchen, 20mm with a mitre where it shows. For a heavy overhang, 30mm or 20mm with support designed in. And for porcelain, usually 12mm mitred, because that is how the material is made.