The box says 1,000 pieces, but how many go along each side, how many are edge pieces and how long will it take? This calculator works out the grid from the piece count and the finished size.
Rows and columns
Most jigsaw puzzles are cut on a grid where pieces are roughly square. To keep pieces square, the ratio of columns to rows matches the ratio of width to height:
columns ≈ √(pieces × width ÷ height), rows ≈ pieces ÷ columns
A 1,000-piece puzzle of 27 × 20 in gives √(1,000 × 1.35) ≈ 36.7, so 37 columns and 1,000 ÷ 37 ≈ 27 rows. The real grid holds 37 × 27 = 999 pieces. Manufacturers often sell grids that do not land exactly on the round number on the box, such as 38 × 27 = 1,026.
Each piece is about 27 ÷ 37 = 0.73 in, a bit under ¾ in, measured from the center of one knob to the next. Pieces in puzzles for young children are much larger.
Edge pieces
The border is a rectangle of pieces, so:
edge pieces = 2 × (columns + rows) − 4
The 4 is subtracted because corners would be counted twice. For 37 × 27 that is 124 edge pieces, about 12% of the puzzle. Sorting them out first and building the frame is the classic first step.
How long will it take?
Speed varies a lot with the image, the cut and experience. Casual puzzlers often place 50 to 100 pieces an hour on a 1,000-piece puzzle; competition puzzlers finish a 500-piece puzzle in under an hour. Large areas of sky or sea slow everyone down, and speed often increases toward the end as fewer pieces remain. At 100 pieces an hour, a 1,000-piece puzzle takes about 10 hours.
Space to work
Plan a table about twice the area of the finished puzzle, or about 7.5 sq ft for a 27 × 20 in puzzle, to sort pieces by color and shape. A puzzle mat or a large board lets you roll it up or move it between sessions.
Gluing and framing
To keep a finished puzzle, apply puzzle glue on the front, let it dry flat, then frame it. Measure the real finished size, which can be a few millimeters off the box.