Bingo Card Generator

A bingo card generator builds cards in the 75-ball format played across North America: a 5 by 5 grid under the letters B, I, N, G, O, where each column draws from its own block of 15 numbers. Column B holds 1 to 15, I holds 16 to 30, N holds 31 to 45, G holds 46 to 60, and O holds 61 to 75, so the letter called with each ball always tells a player which column to scan.

Each column is filled by shuffling its 15 numbers with a Fisher-Yates shuffle and keeping the first five, so no number repeats within a column and their order is random. The free space, when enabled, replaces the center square of the N column and counts as already marked. That leaves four live numbers in N, and any line through the center needs only four calls. With the free space, each of the B, I, G, and O columns can be filled 15 x 14 x 13 x 12 x 11 = 360,360 ordered ways and the four live N squares 15 x 14 x 13 x 12 = 32,760 ways, about 5.5 x 10^26 distinct cards, so a repeated card within a printed batch is effectively impossible, although the generator does not check for one.

The shuffle runs on a seeded generator: a deck code of up to 12 letters and digits is hashed into the starting state, and every card is drawn from that one stream in order. The same code therefore rebuilds the same cards on any device, and a larger batch under the same code keeps the earlier cards as its first ones, so card 7 of a 20-card deck is card 7 of the 100-card deck too. A blank code gets a new random six-character code on every Generate. Each card carries its deck code and card number, which is how a caller confirms that a claimed card is genuine.

The caller draws one ball at a time, uniformly at random from the numbers not yet called, so no number repeats until all 75 are out. Each call is shown with its letter, the history is kept in call order, a board of all 75 numbers shades the called ones, and matching squares on the on-screen cards are shaded as well. Undoing a call returns that ball to the pool, auto-call draws on a fixed interval until paused or until the pool is empty, and calls can be spoken through the browser's speech synthesis where it exists. The winner check marks a card's squares against the calls, with the free space always marked, and tests the chosen pattern: any of the 12 lines (five rows, five columns, two diagonals), the four corners, the X formed by both diagonals, or a blackout of every square. A line through the free space needs four calls, the X needs eight, and a blackout needs all 24 numbers on the card.

The PDF is drawn as vector lines and text in the built-in Helvetica font, so it stays sharp at any zoom and prints at the printer's full resolution. Pages are Letter (612 by 792 points) or A4 (595 by 842 points) with half-inch margins, holding one card in portrait, two side by side in landscape, or four in a 2 by 2 grid with dashed cut lines. Every grid cell is a true square in the PDF, the PNG, and on screen, and free-space text wraps and shrinks to fit inside its square. Helvetica covers Western European characters only; anything else in the title or free-space text prints as a question mark in the PDF, while the PNG keeps it. The PNG export saves one 1320 by 1728 pixel image per card, 4.4 by 5.76 inches at 300 DPI.

Every number in a column lands on a given card with probability 5/15 = 1/3, because the card keeps five of that column's fifteen numbers. When B-7 is called in a game with six cards, about 6 x 1/3 = 2 cards are expected to hold it. With the free space on, the N column keeps only four numbers, so a call such as N-40 appears on a given card with probability 4/15, about 26.7 percent. On a Letter page holding four cards, each card is 252 points (3.5 inches) wide, so every square is 252 / 5 = 50.4 points, or 0.7 inches, on a side.

Bingo cards serve a wide range of events beyond traditional game nights. Generating custom cards on demand removes the need to purchase pre-printed sets and lets organizers tailor details to the occasion.

• Family Game Night: Print four to eight unique cards for household members and run the built-in caller from a phone or tablet placed at the center of the table, with auto-call and spoken calls doing the work of a cage and a caller.
• Classroom Rewards: A set of cards for students and a called round during a review session turns practice into a game. Winners earn small prizes, and the randomized cards ensure fair play across the class.
• Fundraiser Events: Charity organizers print up to 100 cards, four to a Letter page, with a custom title matching the event branding. The deck code printed on every card lets the caller rebuild the deck on a laptop and verify each claimed win against the calls before paying out.
• Senior Center Activities: Activity coordinators generate one large card per page with the free space enabled for readability. The shaded call board helps participants who missed a call verify their cards, and an undo corrects a mistaken call without restarting the game.
• Office Team Building: Print a set during a lunch break and run a round in the break room. A card title carrying the company name adds a branded touch, and the same deck code reprints a lost card exactly.
• Holiday Parties: A seasonal word such as "JOY" or "LUCKY" in place of "FREE" fits the theme. PNG files, one per card, can be sent digitally to remote guests who play along on screen.
• Bridal and Baby Showers: A card title carrying the guest of honor's name turns printed cards into a personalized party activity. Two cards per landscape page halve the paper while keeping each card large enough to mark comfortably.