Infield Mix and Conditioner Calculator

The arc radius is the whole argument

An all-dirt infield is a sector of a circle, so its area carries the radius squared. That single fact explains most of the surprise on an infield renovation invoice. Struck at 65 feet through a quarter turn, the skin is about 3,318 square feet. Struck at 70 feet, it is about 3,848. Five feet of radius, eight percent more distance, sixteen percent more area — because 70 divided by 65, squared, is 1.16.

Run that through four inches of mix at a fifteen percent bulking allowance and 1.35 tons a cubic yard and the 65 foot arc wants about 63.60 tons. The 70 foot arc wants about 73.76. Ten tons and change is a separate delivery on most jobs.

Tons in that column are at 4 inches compacted, a 15 percent bulking allowance and 1.35 tons a cubic yard, which are the defaults in the form. Change any of the three and the column moves with it.

Grass infields are measured as strips and circles

When there is turf inside the base paths, the skinned area is a set of separate pieces: four strips running base to base, a circle around home, three cutouts at the bases, and often a circle at the pitching area. The trap is counting the strips at their full base-to-base length and then adding the circles on top, which counts the ground where a strip runs into a cutout twice.

This calculator takes the circle radii back out of the strip length before it multiplies by width. Four 60 foot legs is 240 feet of running distance; take out a 13 foot home radius at each of the two legs that touch home, and 13 feet at each end of the base cutouts, and the strip that is actually paint-free skin is shorter than the diamond. What is left is multiplied by the strip width, and the circles are added whole. It is close rather than exact, because a real cutout meets a real strip on a curve.

Compacted depth against loose volume

The depth you enter is the finished depth after the mix has been graded, watered and rolled. Loose material arrives at more volume than that and loses it in place, which is why there is a bulking allowance. Fifteen percent is a starting point, not a property of your product: a high-clay mix that arrives damp moves differently from a sandier blend that arrives dry, and how hard the roller works changes it again.

Weight is where suppliers actually sell, so the last step is tons per cubic yard, which is a number the supplier has for their own product. It is a field here rather than a constant because it moves with the clay fraction and, quite a lot, with the moisture in the pile on the day the truck loads. Two suppliers quoting the same nominal blend can be a tenth of a ton a yard apart.

Conditioner is thin and still heavy

A quarter of an inch of calcined clay across a 3,318 square foot skin is 69 cubic feet. In half-cubic-foot bags that is 139 bags, which is most of a pallet, for a layer you can barely see. This is the number that catches out a first-time topdressing order: the depth sounds trivial and the bag count does not.

Conditioner is a surface management layer. It holds moisture at the very top of the profile and gives the skin something to shed water into, and it is not structural. Going deep with it makes the surface loose rather than firm.

What this does not decide

It does not tell you what a good infield mix is, what ratio of sand to silt to clay suits your climate and your maintenance budget, or whether the profile under the skin will drain. Those are questions for a sports turf agronomist and for the supplier who blends the product, and they depend on things a form cannot see.

Nor does it tell you what the arc radius or the base path should be. Those come off the rule book your league plays under and the layout drawing for your facility, and they differ by level and by organisation.

Why no dimension on this page is a specification

Every distance here is something you type in. That is deliberate. Base paths, arc radii, goal sizes, line widths, run-off margins and safety zones are not universal numbers: they differ between youth, high school, college and adult play, between the organisations that sanction those games, and between one facility standard and the next. A page that hard-coded any of them would be wrong for most of the people reading it and would sound authoritative while being wrong.

So the rule book that governs your league is the authority on the dimension, and the facility standard your grounds department works to is the authority on how much room goes around it. Measure the field you actually have, take the target dimensions off the document that governs your play, and put those numbers in the form. What this calculator does is the arithmetic that follows.

Before anything goes into the ground

Irrigation mains, drainage, electrical runs to scoreboards and lighting, and old utility crossings all live under sports fields, frequently at shallow depths and frequently not where the as-built drawing says. Call 811 before you dig, trench, drive a stake, auger a post or set an anchor, and give the locate time to be marked. Private lines on the facility side of the meter are usually not covered by the public locate service, which is what catches out a crew that did everything else right.

Open fields are also the place people get hurt by heat and by machinery. A groundskeeper on a mower or an aerator in July is exposed on both counts at once, and neither risk announces itself.

Related pages: the pitching mound clay calculator handles the mound and the plate areas, the aeration and topdressing calculator covers the turf side of the same field, and the gravel calculator is the general tool for bulk material by the ton. For the batting cage behind the backstop, the batting cage net calculator sizes the netting.

Questions people ask