Tree Root Ball Diameter and Weight (ANSI Z60.1)

Scopeat roughly ten to twelve inches of ball diameter per inch of caliper for a shade tree, with the depth a fraction of the diameter rather than a sphere -- a ball is dug flat-bottomed and wide, because that is where the roots are. THE WEIGHT IS THE NUMBER PEOPLE GET WRONG, AND BY A WIDE MARGIN. A six inch caliper tree carries a five foot ball three feet deep, and at the density of moist loam that is about three tons of soil before the tree above it (a tapered ball weighs less than this flat-bottomed cylinder; UT Extension prints 2.4 tons for a 60 by 32 in ball). It is a crane or a large tree spade rather than a crew and a cart, and it is a number worth having before the delivery arrives rather than when it is sitting on the truck. WEIGHT GOES AS THE CUBE OF CALIPER at a fixed ratio, because the diameter, the depth and the width all scale with it -- so doubling the caliper is eight times the weight, and the handling method changes long before the tree looks twice as big. The caliper a given handling limit will carry is reported for that reason: it is the specification question, asked in the direction the site can answer. The trade the ratio represents is survival against handling. A larger ball retains more of the root system and transplants better, and every inch of it costs weight, equipment and money -- which is why the standard gives a range rather than a number, and why a specification that cuts the ball to what the equipment can lift has traded survival for a delivery. Soil density is the other lever and it is not a choice: a ball dug wet is far heavier than the same ball dug in normal moisture, and irrigation before digging is a real and often overlooked contributor to a lift that will not go. A volume and a weight from the standard's proportions. It does not select the ball size, which the specification and the standard do by species and by whether the tree is balled-and-burlapped, in a container, or spaded; the proportions differ for conifers, for multi-stem plants and for large-caliper stock. It does not address the rigging, the lifting points, or the fact that a root ball must be lifted by the BALL and never by the trunk, which breaks the root-soil bond and kills trees that arrive looking fine. It does not evaluate planting depth -- the root flare goes at grade and a ball set too deep is a slow failure -- backfill, staking, or aftercare irrigation, which decides survival more than any of this. ANSI Z60.1, the project specification, and a qualified arborist or nursery professional govern.

Formula or tableball diameter = trunk caliper x the entered inches of ball per inch of caliper; ball depth = that diameter x the depth ratio; volume as a flat-bottomed cylinder pi/4 d^2 h; weight = volume x soil density; and the caliper a handling limit carries is the cube root of that relation.

Source and editionThe ANSI Z60.1 root ball proportions by name -- roughly 10 to 12 in of ball diameter per inch of caliper for shade trees, with the depth commonly 0.60 to 0.75 of the diameter -- and moist loam at roughly 100 to 110 pcf. The proportions differ for conifers, multi-stem plants and large-caliper stock and are entered. It does not address rigging, lifting by the ball rather than the trunk, planting depth, backfill, or aftercare. ANSI Z60.1, the project specification, and a qualified arborist or nursery professional govern.

Free accessOne cylinder volume and one density; no ANSI table is reproduced.

What governsEstimate. AHJ and licensed professional govern.

API field namescaliper_in, ball_per_caliper_in, depth_ratio, soil_density_pcf, handling_limit_lb, ball_diameter_in, ball_diameter_ft, ball_depth_ft, ball_volume_ft3, ball_weight_lb, ball_weight_tons, caliper_for_limit_in

• Proportions are entered per stock type conifers, multi-stem and large-caliper stock differANSI Z60.1
• No rigging or lifting method a ball must be lifted by the BALL, never by the trunka qualified arborist
• No planting depth or aftercare the root flare goes at grade, and irrigation decides survivalthe project specification