Soft Wash Mix Calculator
Pick your batch tank size and the strength off our Softwash Percent Guide, and the calculator tells you how many gallons of 12.5% sodium hypochlorite and water to batch. Surfactant is an additive, so it gets its own step underneath.
Built for batch mixing with a dedicated soft wash pump, whether that’s a 12 volt, a gas unit, or any other pump that pulls straight out of a batch tank. It handles batches up to 100 gallons; for a bigger tank, run it twice.
Mix calculator
Gallons of 12.5% sodium hypochlorite and water for one batch tank, for any dedicated soft wash pump: 12 volt, gas, or otherwise.
- 12.5% SH—
- Water—
Fill order: water first, then SH, then your surfactant last so the tank doesn’t foam over.
For batch mixing with a dedicated soft wash pump that draws from a batch tank. If you downstream instead, the injector dilutes this batch again on the way to the surface.
Then add surfactant
Surfactant is an additive. It goes in on top of the batch and doesn’t change the bleach and water numbers above.
Soft wash dilution chart: 12.5% SH by tank size
These are the batch numbers behind the calculator for the three most common tank sizes: gallons of 12.5% sodium hypochlorite, then gallons of water. Every strength matches the Softwash Percent Guide.
| Mix strength | 25 gal batch | 50 gal batch | 100 gal batch | SH to water |
|---|---|---|---|---|
| 1% | 2 gal SH, 23 gal water | 4 gal SH, 46 gal water | 8 gal SH, 92 gal water | 1 : 11.5 |
| 2% | 4 gal SH, 21 gal water | 8 gal SH, 42 gal water | 16 gal SH, 84 gal water | 1 : 5.25 |
| 3% | 6 gal SH, 19 gal water | 12 gal SH, 38 gal water | 24 gal SH, 76 gal water | 1 : 3.2 |
| 4% | 8 gal SH, 17 gal water | 16 gal SH, 34 gal water | 32 gal SH, 68 gal water | 1 : 2.1 |
| 5% | 10 gal SH, 15 gal water | 20 gal SH, 30 gal water | 40 gal SH, 60 gal water | 1 : 1.5 |
| 6% | 12 gal SH, 13 gal water | 24 gal SH, 26 gal water | 48 gal SH, 52 gal water | 1 : 1.1 |
The math for any tank size: gallons of SH = tank size × target % ÷ 12.5, and water is whatever is left. A 65 gallon batch at 2% is 10.4 gallons of SH (10 gallons plus a quart and a half) and 54.6 gallons of water. Strength means the sodium hypochlorite percentage in the finished mix, after it has been cut with water.
Which strength to use: the Softwash Percent Guide
These are the same strengths printed on our Softwash Percent Guide. When in doubt, start at the lower percent and test a small spot first.
| Strength | Surfaces and materials |
|---|---|
| 1% | Vinyl siding, painted substrates, stained decks, fiberglass structures, fabric awnings, playground sanitation |
| 2% | Vinyl siding, brick with light growth, metal roofing, Dryvit and stucco, TPO membrane roofing, pre-treating flatwork |
| 3% | Brick with severe growth, Dryvit and stucco with medium staining, stone, tile roofing with light staining, pre-treating flatwork, general test spot |
| 4% | Asphalt shingle with light staining, TPO membrane roofing with severe growth, Dryvit and stucco, tile roofing, pre-treating flatwork, general test spot |
| 5% | Asphalt shingle with medium staining, Dryvit and stucco with severe staining, tile roofing with severe staining, lichen and moss, tannin stains from leaves and acorns |
| 6% | Asphalt shingle with heavy staining, tile roofing with severe staining, lichen and moss, concrete driveways (soft wash only), tannin stains from leaves and acorns |
Adding surfactant
Surfactant is an additive, not part of the bleach-to-water ratio. It goes in last, on top of the finished batch, and it is measured per gallon of mix, bleach and water together. It gives the mix cling so the SH has time to work instead of sheeting off the surface, and it covers the bleach smell.
- Apple Suds: ½ to 1 oz per gallon of mix
- Lemon Suds: ½ to 1 oz per gallon of mix
- Cherry Suds: ¼ to ½ oz per gallon of mix. It is double thick, so it takes half as much
Start at the low end and add until you get the cling you like. A 100 gallon batch at ½ oz per gallon takes 50 oz, a little over a quart and a half. Fill order is water first, then SH, then surfactant, so the tank does not foam over.
Batch mixing vs. downstreaming
This calculator is for batch mixing: you build the finished mix in a tank, and a dedicated soft wash pump, 12 volt, gas, or otherwise, sprays it straight onto the surface at that strength. Downstreaming is different. The injector on your pressure washer pulls from a concentrate tank and dilutes it again with the machine’s water on the way to the surface, so a downstream tank has to be mixed hotter to land at the same strength. If you downstream, treat these numbers as the strength you want on the surface, not the strength in your tank, and read our downstreaming guide for how injectors draw.
Fresh bleach matters
Sodium hypochlorite loses strength with heat and time. A drum that has been riding in the truck through summer can test well under 12.5%, which means every batch comes out weaker than the chart says. Buy from a supplier who turns inventory, keep it cool and out of the sun, and if a mix is not performing, suspect the bleach before you suspect the ratio. Local to Portland? We stock fresh SH by the gallon for pickup at our Oregon City shop.
Keep reading
- How a soft wash mixing system actually works
- Remco 5.3 GPM vs 7 GPM: we tested the distance
- 12V soft wash pumps and soft wash systems and parts
- Pressure washing and soft wash chemicals
- Hands-on soft wash training at our Oregon City shop
Common questions
How much 12.5% bleach do I need for a 1% house wash mix?
Take the tank size, multiply by 1, and divide by 12.5. A 100 gallon batch is 8 gallons of 12.5% sodium hypochlorite and 92 gallons of water; a 50 gallon batch is 4 and 46. Surfactant goes in on top of that at ½ to 1 oz per gallon of mix.
What percentage should I use for a roof wash?
On the Softwash Percent Guide, asphalt shingle runs from 4% for light staining up to 6% for heavy staining, and tile roofing from 3% to 6% depending on how bad it is. Start at the lower end, test a small spot, and step up only if it isn’t killing the growth.
Does the surfactant change my bleach-to-water ratio?
No. Surfactant is an additive measured per gallon of finished mix, bleach and water together. It goes in last, after the water and SH, so the tank doesn’t foam over.
How much surfactant goes in a batch?
Apple Suds and Lemon Suds run ½ to 1 oz per gallon of mix. Cherry Suds is double thick, so it runs ¼ to ½ oz per gallon. A 100 gallon batch at ½ oz per gallon takes 50 oz, a little over a quart and a half. Start at the low end and add until you get the cling you like.
Can I use these numbers if I downstream?
Not directly. A downstream injector dilutes your tank mix again with the machine’s water on the way to the surface, so a downstream tank has to be mixed hotter to land at the strength you want. These numbers are for batch tanks fed by a dedicated soft wash pump: 12 volt, gas, or otherwise.
Why does my mix seem weaker than the chart says?
Most of the time it’s the bleach. Sodium hypochlorite loses strength with heat and age, so a drum that has been riding in a hot truck can test well under 12.5%. Buy fresh, keep it cool and out of the sun, and suspect the bleach before you suspect the ratio.
Can I mix a batch the night before?
You can, but it keeps losing strength once it’s mixed, faster in heat and sunlight. Mix close to when you’ll spray it and keep the tank covered.
What order do I fill the tank?
Water first, then the 12.5% SH, then the surfactant last. Adding soap before the water foams the tank over.
