Cost per Pound & Profit
Enter your substrate, spawn, bag, labor, and utility cost per block, your contamination rate, and your fresh yield — get the true cost per pound, profit per block, and margin at your sale price. Contamination isn't a footnote here; it's rolled straight into the number, the way it actually hits your bottom line.
cost/lb = (cost/block ÷ (1 − contam%)) ÷ yield/block. Every failed block's cost is spread over the survivors, then divided by pounds — that's your real cost per pound, not the pre-contamination one.
Find your real cost per pound — contamination included.
Cost per pound = effective cost per good block ÷ yield per block, where the effective cost spreads every failed block's expense over the blocks that actually fruited. Most growers price off a spreadsheet that adds up substrate, spawn, and labor and stops there — then wonder why the bank account doesn't match the math. This tool rolls contamination loss into the cost itself, the way it actually hits you, and hands back the four numbers that decide whether you're running a farm or a hobby: cost per pound, profit per block, margin, and break-even price.
Everything runs client-side. Nothing is stored, nothing is sent — change any input and the result updates live.
The cost-per-pound formula, explainedThe math behind the number.
Cost per block, then spread across contamination
Start by adding up everything that goes into one block: substrate, spawn, bag and filter, labor, and utilities/sterilization. That's your cost per block — but not every block makes it to harvest. If 10% contaminate, the survivors have to carry the cost of the ones that didn't. Divide by (1 − contamination rate) to spread that loss across the good blocks, then divide by pounds of fresh yield to get cost per pound.
costPerBlock = substrate + spawn + bag + labor + utilities
# failed blocks' cost spreads over the survivors
effCostPerGood = costPerBlock ÷ (1 − contam/100)
costPerLb = effCostPerGood ÷ yieldLb
# then the economics at your sale price
revenuePerBlk = yieldLb × price
profitPerBlk = revenuePerBlk − effCostPerGood
margin = profitPerBlk ÷ revenuePerBlk × 100
breakEvenPrice = costPerLb
Why break-even equals cost per pound
Break-even price is just the sale price where profit hits zero — which by definition is the same number as your cost per pound. If you're selling below that price, every pound sold loses money regardless of volume; selling above it, every additional pound is pure margin above the fixed recovery point. That's why the calculator surfaces it as its own line: it's the floor, not a nice-to-know.
Default inputs. Substrate $2.00 + spawn $1.00 + bag $0.50 + labor $1.50 + utilities $0.50 = $5.50/block.
At 10% contamination: effective cost = $5.50 ÷ 0.90 = $6.11 per good block.
At 1.5 lb/block fresh yield: cost = $6.11 ÷ 1.5 ≈ $4.07/lb — that's the true cost, and the break-even price.
At $12/lb sale price: revenue = 1.5 × $12 = $18.00/block. Profit = $18.00 − $6.11 ≈ $11.89/block, margin ≈ 66%.
When the standard number is wrong.
The formula is simple. Here's where the "just add up costs" version quietly costs you money.
Contamination is a cost multiplier, not a footnote
Every failed block spreads its cost over the survivors — 10% contamination adds ~11% to your real cost per pound (dividing by 0.90 is the same as multiplying by 1.111). Go to 20% and it's a ~25% add-on. This is exactly where the ROI of a flow hood, a better sterilizer, or tighter technique lives: it isn't a soft "quality" improvement, it's a direct line to your cost per pound and your margin.
Labor is the hidden majority at small scale
If you're not paying yourself a real wage in this calculator, your "profit" is just an unpaid wage wearing a nicer name. Put an honest number in the labor field — what you'd have to pay someone else to mix substrate, inoculate, tend fruiting rooms, and harvest — before you trust the margin this tool reports. A farm that looks profitable on paper because labor is priced at zero isn't profitable; it's a job that hasn't billed itself yet.
Yield moves cost per pound more than price does
Doubling your yield per block — through better biological efficiency and more consistent flushes — roughly halves your cost per pound. Raising your sale price by the same percentage rarely survives contact with the market the way a real yield gain does. Chase yield (dial it in with the Biological Efficiency calculator) before you chase a higher price tag.
Cost per pound isn't the only metric that matters
Most of a block's yield comes in the first flush. Composting a block after flush one to free up shelf space faster will usually raise your cost per pound — but it can raise dollars per square foot per week, which is the number that actually caps your farm's revenue at a given footprint. Track both. A slightly worse cost per pound that turns your space over twice as fast can out-earn a lower cost per pound sitting on shelf space for an extra month.
Notes from the farmThe first year I ran real numbers on this, the spreadsheet said I was profitable and the bank account disagreed — because the spreadsheet didn't know about contamination, and it definitely didn't know I'd priced my own labor at zero. Once I put a real wage in and rolled contamination into cost per pound instead of treating it as a shrug-and-move-on loss, the picture got a lot more honest, and a lot more useful: I could finally see that a bad sterilizer cycle wasn't just "some blocks didn't make it," it was a specific, quantifiable hit to every pound I sold that week. Price off the number that includes your failures — that's the number the market actually pays against.
Track cost per pound against every batch and flush.
A cost-per-pound calculation is a snapshot. The value shows up when you log actual costs, yields, and contamination against batch, flush, and grow room across every harvest — and see which rooms are quietly drifting before a crop is lost. That's what a Farm-Ops tracker does automatically.