Free online Shikaku puzzles (also known as Sikaku, Rectangles or Divide by Box) with no ads and no sign-up. Pick a 5×5, 7×7, 10×10 or 15×15 grid or play the daily 10×10 puzzle; every puzzle is generated fresh and checked to have exactly one solution. Your game saves itself as you play, on phone and desktop, so you can put it down and come back. Solved puzzles count towards the leaderboard, with a second board for the fastest 10×10 times. The rules fit in a sentence: divide the grid into rectangles so that every rectangle contains exactly one number, and that number is the rectangle's area in cells. Every cell must end up inside a rectangle. Tap two opposite corners (or drag) to draw one, tap a rectangle to select it and erase it, and undo any move. If you get stuck, the candidates toggle outlines every rectangle a chosen number could still be.