Supporting partner’s opened (major) suit is highest priority for responder. Normally he will have four+ cards to support [although he can raise 1 /♠ to 2 /♠ with three cards, when the alternative is the ‘dustbin 1 NT’]. The higher he bids, the better his hand. Here is the
Responder’s Support Line:

In addition to his point-count, responder should factor in his shape. In particular, shortage (ruffing potential) is very powerful. A doubleton is worth (about) one extra point,
a singleton three and a void five. Having a fifth card in support is also huge: worth (at least) one extra point. Having said all that, though, I should say that the more you play, the less you should compute such strictures and the more you should use your judgement, or ‘feel’.

Exercise: Partner opens 1 ♠. How many would you bid in support with:

Hand (i): Respond 3 ♠, showing four-card support and 10-12 points.

Hand (ii): Respond 3 ♠. Although you have only seven high-card points, the singleton heart is worth about three extra points.

Hand (iii): Respond 4 ♠. The void is worth about five extra points and the fifth spade is also worth a point or so.

Hand (iv): Respond 2 ♠. Showing 6-9 points and often just three card-support (preferably decent – ie headed by a picture).

Click here to play this deal.