SH mix ratio calculator
Stock strength in, target strength and batch size in, gallons of SH and water out. The math is shown so you can check it on the tailgate.
Your batch
Common targets
What operators commonly run at the surface. Chemical labels, your local rules and the surface in front of you win over any table. These are starting points, not instructions.
| Surface | Target % | From 12.5% stock | From 10% stock | Notes |
|---|
The math
Gallons of SH = batch gallons × target % ÷ stock %
Water = batch − SH
Ratio = 1 : (stock ÷ target − 1)
Example: 50 gallons at 2% from 12.5% stock is 50 × 2 ÷ 12.5 = 8 gallons of SH and 42 of water, a 1 : 5.25 ratio. Downstream injectors dilute again at the gun (commonly 10 : 1 to 20 : 1), so if you batch for a downstreamer, mix the tank stronger by that factor: a 2% target through a 10 : 1 injector needs a 22% tank, which 12.5% stock cannot reach. That is why house-wash downstreaming tops out around 1% and roof work is done with a pump.
Safety, briefly
- SH bleaches skin, clothes and plants. Gloves, eye protection, and pre-wet and rinse landscaping.
- Never mix SH with acids or ammonia products. Chlorine gas.
- Stock strength drops in heat and sunlight. A jug that sat in the truck for a month is not 12.5% any more. The calculator assumes the number you type.
- Runoff rules vary by city. Know yours before a roof job.
Now price the job
Chemicals are usually 5 to 10% of the ticket. The bigger number is what you charge for the surface. The calculator gives the 2026 market range, your cost floor and $/hour for a house wash, roof, driveway or deck in about a minute.