What Is the Blackwood Convention in Bridge?

Blackwood is a slam-bidding convention in which a bid of 4NT asks partner one question: how many aces do you hold? Partner answers 5♣ with zero or all four, 5♦ with one, 5♥ with two, and 5♠ with three. The whole point is to make sure you never bid a slam while the opponents are sitting there with two aces to cash.

By Tracey Bauer

New to bridge? Start with the complete beginner’s guide, then come back for slam bidding.

Blackwood is the most famous convention in bridge, invented by Easley Blackwood in 1933 and still on almost every convention card in the world. It is also one of the most misused. Here is how it works, when it wins, and when it quietly costs you a slam.

What problem does Blackwood solve?

A small slam means committing to twelve of the thirteen tricks. There is exactly one disaster that no amount of skill can play around: the opponents cash two aces before you ever gain the lead. Down one, cold, in a contract your point count said you had earned.

High card points measure overall strength, but they cannot tell you which specific cards partner holds. Two partnerships can each hold 32 HCP, and one of them is missing two aces. Blackwood removes the guess. Once the partnership knows a slam is likely on power and fit, one player bids 4NT, counts the aces in the answer, and either bids the slam or stops safely at the five level.

The 4NT bid says nothing about notrump. Like the Stayman 2♣, it is a question, not a place to play.

How does classic Blackwood work?

After the partnership has agreed a trump suit and shown slam-going strength, a bid of 4NT asks for aces. Partner has four answers:

• 5♣ = zero aces, or all four
• 5♦ = one ace
• 5♥ = two aces
• 5♠ = three aces

The 5♣ answer doing double duty sounds alarming, but it never causes confusion in practice. A hand that could not produce a single ace and a hand holding all four are so far apart in strength that the earlier auction always tells you which one partner has.

The asker then adds partner’s aces to their own and decides. Holding all four aces or missing just one, bid the small slam. Missing two aces, sign off in five of the agreed suit, and partner is required to pass. The convention did its job: you found out for the price of one bid, and you stopped in time.

What is the 5NT king ask?

After the ace responses, a follow-up bid of 5NT asks partner how many kings they hold, using the same ladder one level higher: 6♣ with zero or four, 6♦ with one, 6♥ with two, 6♠ with three.

The 5NT bid carries a guarantee that matters more than the answer: it promises the partnership holds all four aces. You only ask about kings when you are considering all thirteen tricks, so 5NT is a grand slam invitation. That guarantee lets a responder with a maximum and a source of tricks simply bid the grand slam instead of answering. Never bid 5NT casually. If a small slam is your ceiling, bid it and put the dummy down.

When should you not use Blackwood?

This is the lesson club players rarely get taught, and it is where the convention earns its reputation for backfiring. Blackwood answers exactly one question, how many aces, so it is the wrong tool whenever that answer will not settle the hand.

• Two fast losers in an unbid suit. Holding something like 7 4 in a suit nobody has bid, hearing “one ace” does not help, because you cannot tell whether it is the ace you need. The opponents may still cash the ace and king of your weak suit. Hands like this want a control-showing cue bid, not Blackwood.
• Minor-suit agreements that crowd the safety level. When clubs are trumps, your safety net is 5♣, and every Blackwood response except 5♣ has already driven past it. Diamonds are only slightly better. Ask with care, or use a different slam tool, when a minor is trumps.
• Voids. A void is not an ace, and aces opposite a void can be wasted. Blackwood counts aces without knowing where they live, so freak shapes call for cue bidding instead.

What does a Blackwood auction look like?

South opens 1♠ holding:

♠ A K Q 8 4   ♥ K Q J 5   ♦ K Q 4   ♣ 7   (20 HCP)

North raises to 3♠, a limit raise showing four trumps and 10 to 12 points, with:

♠ J 9 5 2   ♥ A 8 3   ♦ A 7 6   ♣ K 8 4   (12 HCP)

The auction: 1♠ - 3♠ - 4NT - 5♥ - 6♠.

South can count 32 combined points and a nine-card spade fit, so slam is in the picture. The only question is aces, and this hand is the textbook case for asking: no void, and no unbid suit sitting there with two quick losers. South bids 4NT, and North answers 5♥, two aces. South holds one, so exactly one ace is missing, and South bids 6♠. Twelve tricks are there off the top: five spades, four hearts, and three diamonds, losing only the ♣A.

Change one card in the story and the convention shines the other way. If North had answered 5♦, one ace, South would know two aces were missing and sign off in 5♠. That quiet five-level stop is the real payoff of Blackwood, and it never makes the highlight reel.

What is Roman Key Card Blackwood?

Modern partnerships upgrade classic Blackwood to Roman Key Card Blackwood, which counts five cards instead of four: the four aces plus the king of trumps. It can tell you about the queen of trumps as well. Bridge Unleashed teaches the 1430 responses: 5♣ shows one or four keycards, 5♦ shows zero or three, 5♥ shows two without the trump queen, and 5♠ shows two with her.

Notice the trap hiding in that first step. In classic Blackwood 5♣ means zero or four aces. In 1430 keycard it means one or four. Same bid, different message, and a partnership that has not agreed which one they are playing will eventually bid a slam off two keycards. Agree before you sit down. The other common variant, 0314, swaps those first two steps and leaves every other principle intact.

Why bother at all? Because the king and queen of trumps decide slams just as often as a missing ace does. Keycard is a bigger memory investment, and both partners have to be on the same page about the responses before it ever comes up at the table. Learn classic Blackwood first, get comfortable, then upgrade together. If the vocabulary here is new, the bridge glossary defines keycards, cue bids and voids in plain language.

Common Blackwood mistakes

• Asking when the answer cannot help. With two fast losers in an unbid suit, or a void, 4NT gives you information you cannot use. Cue bidding is the right tool.
• Forgetting that some 4NT bids are not Blackwood. A direct raise of 1NT to 4NT is quantitative, inviting 6NT on power. Blackwood applies after a suit is agreed. Confusing the two is how partnerships end up passing an ace-ask.
• Bidding 5NT without all four aces. The king ask promises them. Break that promise and partner may bid a grand slam missing an ace.
• Treating the responses as strength. 5♥ shows two aces, not a good hand. The asker is the captain; the responder answers and then does as told.
• Skipping the ask on big hands. Strong auctions, like those starting with the Strong 2♣ opening, head toward slam often, and “we had 33 points” is no comfort when two aces cash. If slam is in the picture, check.

Learn it at the table: slam bidding

Reading about Blackwood gets you the map. Bidding real slams with a partner gets you the territory. Let’s Go Slammin’ is the Bridge Unleashed workshop built around exactly this question: when a slam is actually there, control bids, Roman Keycard Blackwood 1430 with the queen ask and the king ask, quantitative 4NT, Splinters, and Exclusion for the hand with a void. One ticket covers both sessions, the lesson and the Play of the Hand, and both replays are included.

Most workshops are $25, with some at $10 or $15. Browse them all at bridgeunleashed.com/workshops.

Want every workshop, every Play of the Hand session, and every replay in one place? That is the Bridge Unleashed VIP Community.

And if you like learning one convention at a time, the 50 Conventions series delivers a convention a day, with deeper hand examples, auction analysis and the partnership agreements behind each one.

Questions players ask about Blackwood

Is 4NT always Blackwood?
No. A direct raise of a 1NT or 2NT opening to 4NT is quantitative, asking opener to bid 6NT with a maximum. Blackwood applies when the partnership has agreed a trump suit, or clearly implied one, and is heading for slam.

What are the responses to Blackwood?
Over 4NT, partner bids 5♣ with zero or four aces, 5♦ with one, 5♥ with two, and 5♠ with three. The earlier auction always makes clear whether 5♣ means zero or all four.

What does 5NT mean after Blackwood?
It asks for kings on the same ladder one level higher, and it promises the partnership holds all four aces. Because of that promise, 5NT invites a grand slam, and responder may simply bid it with the right extras.

What is the difference between Blackwood and Roman Key Card Blackwood?
Classic Blackwood counts the four aces. Roman Key Card counts five keycards, the four aces plus the king of trumps, and it can locate the trump queen as well. Bridge Unleashed teaches the 1430 responses: 5♣ shows one or four keycards, 5♦ shows zero or three, 5♥ shows two without the trump queen, and 5♠ shows two with her.

When should you avoid Blackwood?
When the answer cannot settle the hand: with two fast losers in an unbid suit, with a void, or when a minor-suit agreement means the responses would push you past your safety level. Those hands call for control-showing cue bids instead.