Five inputs. Instant breakdown: SH stock gallons, water gallons, surfactant ounces, total chemical cost, and cost per square foot.
Competitors don't build this. We do — because chemical costs tracked to the gallon is how operators protect their margins.
What you get instantly
SH stock gallons needed at your target working concentration
Cost per square foot and margin note at $0.35/sqft bid
Email-gated wallet card PDF with mix math reference for your truck
Why Jobber doesn't have this
Jobber, Housecall Pro, and ServiceTitan track jobs and invoices. None of them track chemical cost at the gallon level per job — because they're built for generalist trades. Pressure washing has specific chemistry math (C1×V1=C2×V2 dilution from stock SH), coverage rates that vary by surface and application method, and surfactant dosing that varies by job type. This calculator handles all of it. The margin check at $0.35/sqft is the number most operators never track until they wonder why their margins are shrinking.
The math behind this calculator is the C1×V1=C2×V2 dilution formula — the same one you'd use in a chemistry textbook. Here's how it applies to pressure washing:
Step 1: Total mix gallons. Divide your square footage by the coverage rate for the job type. House wash coverage runs ~50 sqft/gal of diluted mix, roof soft wash ~30 sqft/gal (more saturation needed for organic growth), concrete ~80 sqft/gal, fleet ~60 sqft/gal.
Step 2: SH stock gallons. You know your stock SH concentration (12.5% is standard) and you know your target working concentration (1% house wash, 3% roof). The formula solves for how much 12.5% stock you need to reach your target: SH Stock = (Target% ÷ 12.5%) × Total Mix Gallons.
Step 3: Water gallons. Water = Total Mix − SH Stock. The rest of your tank is water.
Step 4: Surfactant ounces. Multiply the dosing rate by total mix gallons. House wash default is 1.5 oz/gal (standard Elemonator-equivalent ratio). Roof soft wash uses 2 oz/gal for better dwell adhesion.
Step 5: Cost. SH cost = SH stock gallons × your price per gallon. Surfactant cost = ounces × your price per ounce.
Why chemical cost tracking matters for bidding
Chemical cost is typically 8–15% of revenue on a well-bid job. If you're running 25–30% chemical cost, you either underbid the job or over-applied product. Both problems compound over time — over-application also increases your EPA runoff exposure and substrate damage risk. The margin note at $0.35/sqft gives you a quick sanity check: if your cost is over 20% of bid price, the bid needs adjustment before you sign the contract.
Default rates by job type
The defaults in this calculator come from industry practice, not guesswork: house wash at 1% SH is the standard for residential vinyl/painted wood without significant algae; roof soft wash at 3% handles the black streaks (Gloeocapsa magma) that require higher SH concentration and longer dwell; concrete at 0.5% SH handles surface organic matter without chemical etching risk at higher concentrations; fleet wash at 0.5% handles road grime with minimal corrosion risk. Your actual costs will vary based on growth severity, substrate age, and supplier pricing — the calculator handles the variation as long as you enter your real numbers.
Frequently Asked Questions
How much SH stock do I need for a house wash?
For a 1% working concentration from 12.5% stock, you need (1÷12.5) = 8% of your total mix to be SH stock. A 2,000 sqft house wash at 50 sqft/gal needs 40 gallons total mix × 8% = 3.2 gallons of 12.5% SH stock. At $3.50/gal, that's $11.20 in SH alone — plus surfactant. This calculator gives you the exact number in under a second.
What SH percentage should I use for roof soft wash?
Roof soft wash typically runs 2–4% working concentration in the mix, with 3% as the industry standard for residential asphalt shingles with moderate Gloeocapsa magma (the black streaks). Heavy organic growth or heavily weathered shingles may warrant 4%. This calculator defaults to 3% for roof soft wash — adjust up or down based on conditions.
What is a healthy chemical cost ratio for bidding?
Target chemical cost at 8–15% of your bid price. At $0.35/sqft bid and $0.03/sqft chem cost, you're at 8.6% — healthy. Over 20% means you're under-bidding or over-applying. The calculator's margin note shows the ratio at a $0.35/sqft reference point. If your bid is higher, your margin is better than shown.
Does this calculator include chemical cost per square foot?
Yes. Total chemical cost ÷ square footage = cost per sqft. This is the number you need for bid-level cost tracking. The margin note shows it as a percentage of a $0.35/sqft reference bid price — you can adjust the ratio mentally for your actual bid price.
What is the wallet card PDF?
A one-page laminated-format PDF containing your specific job's cost breakdown, the C1×V1=C2×V2 mix formula, and a quick reference table of default rates for all 4 job types. Print it, laminate it, and keep it in every truck so crews aren't doing math on the job site.
How is this different from the SH Mix Ratio Calculator?
The SH Mix Ratio Calculator focuses on dilution ratios and mix volumes from different stock concentrations. The Chemical Cost Calculator adds dollar cost tracking — your actual supplier price for SH stock and surfactant — to produce the total dollar cost and cost per sqft. Use both: ratio calculator for mixing, cost calculator for bidding.