Most of the day-to-day math in composting isn't complicated, but it adds up fast: how big a pad you need, how much water to add to hit a target moisture, how many cubic yards are sitting in a windrow, how many truckloads that turns into. Getting those numbers wrong wastes space, water, and time. CompostBuilder is a free set of planning tools I built to take that math off your plate so you can spend your attention on the operation itself.
Everything below is free to use, works in US customary units (with metric options where it makes sense), and is meant for conceptual planning at commercial and business scale — not a substitute for a stamped design or a permit review, but a fast way to check your assumptions before you commit equipment, labor, or capital. Here's the toolbox, organized by function.
Laying out the site: PadPlanner
Before a single pile goes down, you need to know whether the material you're planning to process actually fits on the ground you have. The PadPlanner lets you design and visualize a pad layout in seconds — windrows or piles, spacing, aisles, and active footprint — so you can see how much throughput a given pad supports and where the pinch points are. It's the tool I reach for first in any feasibility conversation, because the answer to "can this site handle what you want to bring in?" usually starts with the pad.
If your project runs in metric, there's a PadPlanner (Metric) version — the same layout tool in meters and metric tons — so international operators and consultants working in SI units aren't forced to convert everything by hand.
Getting the recipe right: Recipe and Bulk Density calculators
It doesn't matter how high-tech and shiny of a composting system you have. If you don't get the fundamentals right, those systems are going to struggle and most likely fail. Starting off correctly is crucial, and focusing on carbon-to-nitrogen ratio, bulk density, and moisture are key places to start. I have developed two calculators to get you started.
The Recipe Calculator is the main one. You build an initial mix by volume (cubic yards) and it calculates the blended C:N ratio, moisture content, and bulk density of your recipe. That lets you dial in a starting recipe so you can build a test batch in real life. This is done before you move material at scale. It's the natural companion to the recipe advice in the composting operator tips article.
The Bulk Density Recipe Calculator is a lighter-weight sibling for when you only care about volume and bulk density without running the full C:N and moisture picture. Use the full Recipe Calculator when you're designing a mix; use this one for a quick density check or some specific pilots.
Managing moisture: Water Addition and Curing Irrigation
Moisture is the variable that gives operators the most headaches, and to top it off, it changes across the life of a pile. Two tools cover a couple of areas of the composting system.
The Water Addition Calculator answers the everyday question on the active side: given where a pile's moisture is now and where you want it, how much water does it take to get there? That keeps you from guessing with a hose and either drowning the pile or barely moving the needle. Keep in mind that this doesn't take into account how fast the dry material will absorb the water (the absorption rate) — you'll have to figure this out on the field.
The Curing Pile Irrigation Calculator handles the second part of the process, where piles sit longer and the weather can do more of the work. It estimates irrigation needs while accounting for rainfall and evaporation, so you're adding what the pile actually needs to hold its target moisture through curing rather than a flat, one-size guess.
Sizing piles and capacity: Pile Volume and Throughput
Once material is on the ground, the questions turn to "how much is there?" and "how much can this handle?" These two standalone calculators are built into the PadPlanner tool mentioned earlier.
The Pile Volume Calculator estimates the volume of a pile from its shape and dimensions — useful for inventory, for checking how close a windrow is to your equipment's practical limits, or for sanity-checking what's actually sitting on the pad vs what your records say.
The Pile Throughput Calculator looks at what a single pile can process over time. It's a quick way to see the capacity of one pile, which is where any honest conversation about total facility throughput — or a possible expansion — has to start. This is similar to the earlier calculator but it takes time into account. If you're trying to squeeze more out of an existing site, this calculator pairs directly with the improving and expanding a composting facility guidance.
Moving material and hauling: Mass-to-Volume and Outbound Loads
Composting is a materials-handling business, and material gets hauled, moved around, and sold by (at least) two different measures — weight and volume — that rarely match up cleanly because the bulk densities of organic waste (pre and post compost) range widely.
The Mass-to-Volume Conversion tool converts tons to cubic yards (cy) and back, in both US and metric units. That's the everyday translation between a scale ticket (mass, tons) and a pile (volume, cy), or between what a customer orders by the yard (volume, cy) and what leaves your site through the scales (mass, ton).
The Outbound Loads tool estimates how many truckloads a given quantity works out to, based on bucket size and truck capacity. It's handy for counting cubic yards or tons based on a loader operator just counting buckets. It also helps with planning finished-product shipments, scheduling hauling, or giving a customer a better answer on cubic yards and tons. This tool doesn't account for volume settling after a truck is loaded.
Beyond the calculators: Resources
CompostBuilder also includes resources that go beyond pure calculations: a short Compost Project Assessment that scores an existing or planned operation and provides you with recommendations in about five minutes, a Composting Grants Tracker for federal and state funding opportunities, a Compost Reg Navigator for AI-assisted guidance on regulations and compliance for selected states, an interactive Mulching & Composting Map of operations across the US, and a daily Industry News Digest. They're worth a look when you're planning, funding, or benchmarking a project rather than running the numbers on a specific pile.
How to use the suite
None of these tools require an account, and none of them store your data — they're meant to be quick, honest planning aids. A realistic workflow ties several together: size the site with PadPlanner, design the mix with the Recipe Calculator, plan moisture with the Water Addition and Curing Irrigation tools, and use Pile Volume, Throughput, Mass-to-Volume, and Outbound Loads to translate what's on the ground into capacity and shipments.
With good inputs, they'll get you to a defensible first-pass number quickly. When a project moves from planning toward permitting and design, that's where facility design and operator training take over — and where I'm happy to help. Until then, the toolbox is free: start at CompostBuilder.com.