Difference in counters for spoons

Question

I know that there are several types of counters of spoons/cups.

For example, a counter for cup is はい　while another counter is カップ。

Also さじ　and はい are also counters for spoons. What exactly are the differences between these counters?

Answer 1

To count the number of spoons themselves in everyday life, 本【ほん】 is almost always used (eg 5本のスプーン). さじ is rarely used for this purpose today, but occasionally we see "ひとさじのスプーン" used as a bit poetic or literary expression.

To measure the amount of liquid/sugar/etc using a spoon, 杯【はい】 is mainly used (eg スプーン3杯分の砂糖), and さじ is sometimes used alternatively (eg 砂糖3さじ).

Answer 2

杯{はい} is not really a counter for vessels or containers like a cup or a spoon, but for their contents, ie. cupfuls or spoonfuls.

So if you were ordering two cups of coffee, you would use 2杯, if you wanted an empty cup to pour yourself coffee from the pot, you would use カップ.

The character/word 杯 itself might also be used more figuratively in reference to the "fullness" as explained here.