How fall height is measured
Fall height is the distance from the highest designated play surface a child can stand, sit, or climb on, down to the surfacing below, not the equipment's overall height. A slide platform 6 ft off the ground has a 6 ft fall height even if the slide's ladder or the top rail reaches higher, since those are not surfaces meant to be occupied. Measuring this correctly matters because it is the single number that determines which surfacing materials qualify at all.
Why depth is tied to fall height
Playground surfacing works by absorbing the energy of a fall so less of it reaches a child's head, which is what impact attenuation testing (ASTM F1292) actually measures. A given material and depth combination can only absorb so much energy. Below a certain depth, a material simply cannot cushion a fall from a given height adequately, no matter how good the material is in general. That is why CPSC Table 2 pairs each material with both a minimum depth and a maximum fall height it has been tested to protect at that depth, not just a depth on its own.
Why loose-fill needs extra depth up front
The depths in CPSC Table 2 are compressed depths, the depth the material settles to after use and weathering. Loose-fill materials compress at least 25 percent over time, so installing exactly the minimum compressed depth means it will be under that minimum almost immediately. The standard practice is to install about a third more than the compressed figure (a 1.33x multiplier) and expect it to settle down to the required depth, then keep topping it up as it continues to compress and displace, especially under swings and at slide exits where traffic concentrates the wear. Shredded and recycled rubber is the exception: it does not compress the way wood, sand, and pea gravel do, so its 6 inch figure is already the depth to install and maintain, without the extra allowance.
The 6 ft use zone
Surfacing has to cover more than just the ground directly under equipment. CPSC guidance calls for the surfaced fall zone to extend at least 6 ft in every direction from stationary equipment like climbers and playhouses. Moving equipment needs more: swings need extra surfaced distance in front of and behind the seats to cover where a child launches off or lands, and slides need extra distance beyond the exit. Measuring only the footprint of the equipment itself, without the use zone around it, is a common way playground surfacing projects come up short.
Why some materials cap out lower than others
Sand and pea gravel are both rated only to modest fall heights (4 ft and 5 ft respectively) at their tested 9 inch depth, well below wood chips and rubber, both rated to 10 ft. This is not a flaw in the calculator's math, it is what the tested data actually shows for those materials, and it does not change by adding more depth beyond what has been tested. If your equipment's fall height exceeds what your preferred material is rated for, the honest answer is to switch materials, not to guess at a deeper number that has not been tested.
The CCA warning
Do not use wood surfacing made from CCA (chromated copper arsenate) pressure-treated lumber. CCA was phased out of most residential wood treatment specifically because of arsenic exposure concerns, and it has no place in a surface children will be in constant contact with. Use wood mulch or chips sold specifically as playground surfacing rather than repurposed construction lumber scraps of unknown treatment.
What this tool is, and is not
This calculator is a planning reference for comparing materials and estimating quantities against CPSC's published tables. It is not a substitute for impact-attenuation testing to ASTM F1292, ongoing compliance testing to ASTM F2075, or an inspection by a Certified Playground Safety Inspector (CPSI), and it does not account for state or local requirements that may be stricter than the federal guidance. For a public playground, treat this as a starting point for your budget and material comparison, then confirm the finished installation with proper testing and inspection.
For the landscaping around a playground rather than the fall zone itself, the mulch calculator uses the same area-and-depth approach for decorative, non-safety beds. If you are considering rubber mulch specifically, note that this page and the rubber mulch calculator are not interchangeable: this page applies CPSC fall-height depth requirements for safety surfacing, while the rubber mulch calculator is scoped to decorative landscape depth only and should not be used to plan a fall zone.