# Caliper, explained: how shade trees are measured and sold

Published November 2, 2026 by Arboras.

Shade trees are sold by trunk diameter, not height. How caliper is measured, what it says about the root ball and height, and how to read it on a plan.

A plan that calls for "Willow oak, 3 in. cal., B&B" is asking for a tree by the thickness of its trunk. Caliper is how shade trees are sold, and it says more about the tree than its height does.

## How it's measured

Caliper is the trunk's diameter. The nursery standard, ANSI Z60.1, measures it 6 inches above the ground on trees up to 4 inches in caliper, and 12 inches above the ground on bigger trees. Growers measure with a caliper tool or a diameter tape.

## Why shade trees are sold this way

Height depends on how a tree was grown and pruned, and two trees of the same height can have very different trunks and root systems. Trunk diameter tracks the size of the whole tree more consistently, so shade and street trees are specified by caliper.

## What caliper says about the root ball

The standard sets a minimum root ball for each caliper. For shade trees it works out to roughly 10 inches of ball diameter for each inch of trunk:

- about 24 inches across for a 2-inch tree,
- about 32 inches for a 3-inch tree,
- about 42 inches for a 4-inch tree.

A bigger ball means a much heavier tree. A 4-inch tree can weigh well over half a ton, which decides what equipment the crew needs and whether it can reach the hole.

## What it says about height

Only roughly, because it varies a lot by species and how the tree was grown. A 2-inch shade tree is often around 12 feet tall, and a 4-inch tree 16 feet or more.

## What isn't sold by caliper

- **Evergreens** such as arborvitae, holly, and magnolia are sold by height, like a ‘Green Giant’ at 8 to 10 feet.
- **Multi-stem trees** such as river birch clumps and crape myrtles are usually sold by height and number of stems.
- **Shrubs** are sold by container size (#3, #7) or by height and spread.

## Reading a size on a plan

- "3 in. cal. B&B" means a 3-inch trunk, balled and burlapped.
- "2½–3 in. cal." is a range. The quote should say which you're getting.
- A shade tree listed by height alone is worth a question before it's ordered.

## Choosing a caliper

Most residential jobs use 2 to 3 inch trees. Go to 3½ or 4 inches where shade or screening matters on day one, or where a city's tree rules call for a minimum size. Bigger has real costs too: see [what you gain and risk ordering bigger trees](/blog/ordering-bigger-trees/).

We list shade trees up to 4 inches in caliper. [See them by caliper](/plants/).