Enter the canvas size from the kit listing and this calculator gives you the drill count, the hours it will take at your own pace, and whether a kit started now can be finished by Christmas or any other date. It handles the unpainted border most kits have, partial-drill designs and round, square or custom drill sizes, then suggests a light pad and frame that fit.
Common kit sizes (fills width and height):
Assumptions: square drills sit on a 2.5 mm grid and round drills on a 2.8 mm grid (the sizes Diamond Art Club gives; Diamond Dotz round drills are 2.88 mm, so use the custom size for those). A half-inch border is our default guess for a listed canvas size, so measure yours. Paces are presets, not measurements: time yourself for the real number. Partial drills can't be placed, so the grid always rounds down.
How the calculator works
A diamond painting is a grid. Each drill sits in one cell, so the count is just how many cells fit across times how many fit down. Three numbers decide it: the painted size, the drill size and how much of the design is covered.
- Find the painted area. Most listings give the canvas size, and the canvas has a plain border you never cover, so the calculator subtracts the border from each side. Choose "painted design area" if you measured the design itself.
- Count the cells across: width in millimeters ÷ drill size, rounded down. Height works the same way. A part-cell can't hold a drill, so it never rounds up.
- Multiply columns by rows for the drill count, then by the coverage for a partial-drill kit.
- Divide drills by drills per hour for the hours. Days are hours ÷ hours a day, rounded up to whole days.
- For a deadline, divide the hours by the days between your start date and the finish-by date. That's the hours a day you need.
The drill sizes come from the makers. Diamond Art Club's guide to round and square drills gives 2.5 mm for square and 2.8 mm for round. Diamond Dotz's drill guide lists its own round drills at 2.88 mm, plus 2 mm minis and 5 mm drills in its kids' kits. That spread is why there's a custom size: if your kit's chart says something different, use the kit's number. Light pad sizes are the ISO 216 paper sizes (A4 is 210 × 297 mm, A3 is 297 × 420 mm, A2 is 420 × 594 mm).
The pace number is the one to check
No one publishes a measured average for drills per hour, so treat our presets as starting guesses (250 an hour for a first kit up to 600 with a multi-placer). Your real pace depends on the drill shape, how many colors change in a small area and whether you use a multi-placer on big single-color patches. Square drills also take a little more care to line up.
Time yourself instead. Set a timer for 10 minutes, and place drills at your normal pace. Count them, then multiply by 6. Do it on a busy part of the design and again on a plain sky, then use the average. Pick "My own timed pace" in the calculator and type it in.
Diamond painting size chart: drills by canvas size
This chart answers the "how many drills in a 30x40" question for the common sizes. The first two columns assume the whole size is painted. The last two take off a half-inch border on each side, which is closer to what a typical kit listing means by its canvas size.
| Size | Square, full size | Round, full size | Square, ½ in border | Round, ½ in border |
|---|---|---|---|---|
| 20 × 20 cm | 6,400 | 5,041 | 4,761 | 3,844 |
| 8 × 8 in | 6,561 | 5,184 | 5,041 | 3,969 |
| 30 × 30 cm | 14,400 | 11,449 | 11,881 | 9,604 |
| 12 × 12 in | 14,641 | 11,664 | 12,321 | 9,801 |
| 30 × 40 cm | 19,200 | 15,194 | 16,241 | 13,034 |
| 12 × 16 in | 19,602 | 15,660 | 16,872 | 13,464 |
| 40 × 50 cm | 32,000 | 25,276 | 28,161 | 22,477 |
| 16 × 20 in | 32,886 | 26,245 | 29,336 | 23,392 |
| 40 × 60 cm | 38,400 | 30,388 | 34,121 | 27,265 |
| 40 × 70 cm | 44,800 | 35,500 | 40,081 | 31,920 |
| 20 × 24 in | 49,329 | 39,277 | 44,969 | 35,776 |
| 50 × 70 cm | 56,000 | 44,500 | 50,841 | 40,560 |
| 60 × 80 cm | 76,800 | 60,990 | 70,761 | 56,580 |
| 24 × 32 in | 78,975 | 62,930 | 73,162 | 58,448 |
Square at 2.5 mm, round at 2.8 mm. Real kits vary by a few percent with the maker's grid and border. For hours, divide by your drills per hour: a 12 × 16 in round kit at 350 an hour is about 38.5 hours, and our guide to how long a diamond painting takes has the full hours table.
Check the math
We tested the formula against hand-worked examples and one published kit. Open each one to see the steps; the calculator gives the same answers with the same inputs.
30 × 40 cm, design area, square drills: 19,200 drills
300 mm ÷ 2.5 = 120 columns. 400 mm ÷ 2.5 = 160 rows. 120 × 160 = 19,200 drills. At 350 drills an hour that's 54.9 hours, and at 1.5 hours a day, 37 days. With round drills: 300 ÷ 2.8 = 107.1, so 107 columns; 400 ÷ 2.8 = 142.9, so 142 rows; 107 × 142 = 15,194.
12 × 16 in whole canvas, ½ in border, round drills: 13,464 drills, 38.5 hours, 0.54 h a day to make Christmas
Take half an inch off each side: 11 × 15 in painted, which is 279.4 × 381.0 mm. 279.4 ÷ 2.8 = 99.8, so 99 columns. 381.0 ÷ 2.8 = 136.1, so 136 rows. 99 × 136 = 13,464 drills.
At 350 an hour: 13,464 ÷ 350 = 38.5 hours. At 1.5 hours a day: 38.47 ÷ 1.5 = 25.6, rounded up to 26 days.
Deadline: start October 15, 2026, with December 25, 2026 as the finish-by date. That's 17 days left in October, 30 in November and 24 in December before the 25th, or 71 days. 38.47 ÷ 71 = 0.54 hours a day, about 33 minutes. On track.
The same canvas with square drills: 279.4 ÷ 2.5 = 111 columns, 381.0 ÷ 2.5 = 152 rows, 16,872 drills. A 60% partial-drill version of the round kit: 13,464 × 0.6 = 8,078 drills.
40 × 50 cm whole canvas, ½ in border: 28,161 square drills
400 − 25.4 = 374.6 mm and 500 − 25.4 = 474.6 mm. Square: 149 × 189 = 28,161. Round: 133 × 169 = 22,477. The painted area is larger than A3 (297 × 420 mm) and fits A2 (420 × 594 mm), so the calculator suggests an A2 pad or sliding an A3.
Checked against a real kit: 115,360 calculated vs 116,053 listed
Diamond Art Club lists its Lighthouse in the Night kit at 40.6 × 27.6 in with 116,053 square drills (checked October 3, 2026). As a design area with square drills: 40.6 in = 1031.2 mm, ÷ 2.5 = 412 columns. 27.6 in = 701.0 mm, ÷ 2.5 = 280 rows. 412 × 280 = 115,360, which is 693 drills or 0.6% under the listed count. Close enough to trust the formula for planning, and a reminder that a maker's own grid can differ slightly.
What the calculator can't know
It works from a size and a drill pitch, so a few things throw it off. Some round-drill kits print on a 2.5 mm grid with drills that nearly touch, which gives more drills than the 2.8 mm assumption. Borders vary from a narrow strip to more than an inch. Special-shape and AB drills don't change the count, but a crowded design with many color changes slows you down, so the hours are always the soft number. Kit drill bags also include spares, so don't expect the bag count to match the canvas count.
It also doesn't do prices or shipping. Working to a gift date? Check the delivery estimate on the listing before you count on the finish date here.
Using the results
The light pad line compares the painted area with A-series sizes; our light pad guide lists real lit areas by model. The frame line adds a quarter-inch reveal and finds the next standard US frame, and how to frame diamond art covers mats and depth. For a big canvas, our large full-drill kit picks list the sizes, and if you're torn between drill shapes, square vs round explains the trade-off. Write your total drills and hours on the free project log so you can see your real pace next time.
If the deadline check comes back tight, the quickest gain is usually a multi-placer pen for large single-color areas, followed by sorted drill storage so you aren't hunting for codes.
Tools that match common results
- Design fits A4 (up to about 8 × 11 in painted): the Ratukall A4 light pad kit, which has three brightness levels and comes with a stand.
- Design needs A3 (most 12 × 16 in and 30 × 40 cm kits): the Ratukall A3 light pad.
- Deadline looks tight: a pen with multi-placer tips, like the RovyFota resin pen with 3-, 6- and 9-drill tips.
- Lots of colors to keep apart: the ARTDOT 60-slot storage case, which has more than 31,000 Amazon ratings.
Sources: Diamond Art Club drill guide and Lighthouse in the Night listing, Diamond Dotz drill guide, ISO 216 paper sizes. Product details from each Amazon listing. All checked October 3, 2026; the links show the current price on Amazon. How we research · Affiliate disclosure