Depending on the size of your kitchen counters, the ideal length and width is usually 20” by 14”. Longer or wider sizes add unnecessary weight and also make the carving board hard to store. Oversized carving boards can be very difficult to wash if they don’t fit into your kitchen sink. A 20” meat carving board will easily hold a midsize turkey or a 5 lb roast.
As for height or thickness, your carving board should generally be around 0.75” inches. It should be thick enough to sit securely on the counter, but still easy to lift. Thinner boards are much easier to store and wash than thicker cutting boards, but they are also more likely to slip on the counter.