Measure first, shop second. This calculator takes the three numbers that matter most, your tree's height, its width across the lowest branches, and your preferred fullness, and turns them into a shopping and planning list. It runs entirely in your browser: nothing you type is sent anywhere.
Estimate your tree's decorations
Enter your measurements and press Calculate. Results appear here.
These are planning rules of thumb, not guarantees. Your tree's shape and your taste decide the final numbers, and the connection limit printed on your light strings always wins.
How the calculator works
Every estimate uses a simple, open formula, so you can check it or adjust it for your own taste.
- Lights = height in feet × lights per foot. The classic rule of thumb is about 100 mini lights per vertical foot, with 50 for a light look and 150 for a dense one. The string count divides that total by the number of lights on each string and rounds up.
- Ornaments = branch surface ÷ spacing². The tree is treated as a cone. Its side surface is π × radius × slant height, where the radius is half your base width and the slant height is the diagonal from the base edge to the tip. Dividing that surface by the square of the spacing between ornaments, such as 9 inches, gives a count. If the tree stands in a corner, the result is reduced to 60 percent.
- Garland = wraps × half the base circumference × 1.1. The number of wraps is the tree's height divided by the gap between wraps, and each wrap is estimated at half the base circumference since the tree narrows towards the top. The extra 10 percent allows for drape and tucking the ends.
- Skirt or collar = branch width, rounded up, plus a few inches. The covering should reach at least the lowest branch tips. The tool shows a range from your width to eight inches wider, so you can round up to a size you can buy.
- Topper = one-tenth to one-seventh of the height. This is a design rule of thumb, which gives a topper height range that looks balanced.
- Stand water = at least one quart per inch of trunk diameter. A commonly cited guideline from tree-industry groups. Enter the trunk's diameter, only for real trees.
Using the results
Treat the numbers as the start of your list, not the end. Round lights up to whole strings, but check the maximum number of strings that can be connected on the label, and use our lights and fire safety guide for inspection tips. For ornaments, pick a mix of sizes, as described in the ornament guide. For the covering, see skirt vs. collar sizing.
Limits of the estimate
Real trees are not perfect cones. A slim tree needs fewer ornaments than the formula suggests because there is less surface, while a very full tree may take more. Pre-lit trees already have lights, so you only need to add to them. A tree with very open branches may need fewer ornaments but more garland to fill the gaps. If your result looks off compared with what you know about your tree, trust your eye.
Frequently asked questions
Is this calculator accurate for every tree?
It is a planning aid built on a simple cone model, so it is most accurate for full-shaped trees. Slim, pencil or flocked trees can differ by 20 percent or more in either direction, which is why the guides recommend checking the results against your own tree.
Does it save or share my measurements?
No. The calculation happens in your browser and nothing is stored or sent.
How do I measure the width of the tree?
Hold a tape measure straight across the lowest branches, tip to tip, at floor level, after fluffing the branches into their final shape.
Why does it ask for the number of lights per string?
So that it can convert the total into whole strings. Light strings come in set counts, and you cannot buy half a string.
Can I use it for a tabletop tree?
Yes, it works for trees from about 2 feet up. For very small trees, choose the "sparse" settings.
