Pressure Washer Detergent Mixing Calculator

How to use this calculator

Pick the surface you are cleaning, the detergent strength you have, the total amount of finished solution you want to mix, and how you are applying it. The calculator returns the detergent and water volumes to add, a surface-specific dwell time, and a warning if your detergent strength does not suit the surface.

Surface dwell times

Dwell time is how long the detergent sits and works before you rinse. The detergent does the cleaning, so giving it time matters more than turning up the pressure.

Surface	Dwell time	Strength
Vinyl siding	3 to 5 minutes	Light or General; work in shade so it does not dry
Wood deck	3 to 5 minutes max	Light only; Heavy strips sealer
Vehicle	1 to 3 minutes	Vehicle-safe only; rinse panel by panel
Concrete with mildew	10 to 15 minutes	Heavy; reapply if it dries before rinse
Patio	5 to 10 minutes	General or Heavy
Fence (wood)	3 to 5 minutes	Light only; same stain risk as a deck
Brick	10 minutes	General; watch for efflorescence with Heavy
Driveway oil stains	15+ minutes	Specialty degreaser; sometimes 2 to 3 applications

Tips for success

• Dwell and rinse, do not blast. The detergent does the work, not the pressure. Let it sit the recommended time, then rinse with the green 25 degree or white 40 degree tip. Never use the red 0 degree tip on most surfaces.
• Do not let detergent dry on the surface. Sun and wind cause streaks. Work in shade, work in sections, and mist a section with water if it starts drying out.
• Always test an inconspicuous area first. Try a back corner of the deck, the side of the garage, or behind a bush before doing the whole surface.
• Never put bleach in your pressure washer. Sodium hypochlorite corrodes pump seals and injector valves within weeks. Use a separate pump sprayer for bleach, then rinse with the pressure washer using water only.
• Match strength to surface. Vehicle-safe formulas are too gentle for mildewed concrete or oil stains, and Heavy or specialty products strip wood sealer. The compatibility check above flags mismatches before they cost you a finish.

Common mistakes

• Using a vehicle-safe wash on tough surfaces. It is formulated to be gentle, so it will barely touch mildew or oil. Step up to General or Heavy.
• Using Heavy or specialty product on wood. It strips stain and sealer in one pass. Wood decks and fences want Light strength only.
• Letting the detergent dry. Dried detergent streaks and is hard to remove. Keep the surface wet until you rinse.
• Mixing too rich. More detergent is not more cleaning, it just wastes product and leaves residue. Stick to the ratio for your method.
• Pouring bleach into the tank. It quietly destroys the pump. Keep bleach out of the machine entirely.

Canada: detergents, pricing, and water

• Where to buy. Canadian Tire carries Simoniz and Karcher concentrates, Home Hardware stocks Wet & Forget and Krud Kutter, Princess Auto has Spray Nine and commercial concentrates, and Costco Canada sells Karcher concentrate in bulk.
• Pricing. A 1-gallon concentrate runs about USD 15 to 25, or roughly CAD 20 to 35, with the CAD price about 1.35 times the USD figure for the equivalent product.
• Water hardness. Hard water in the prairie provinces, much of Ontario, and parts of the US Midwest reduces detergent effectiveness, so you may need slightly more. Soft water in BC, Atlantic Canada, and the Pacific Northwest means you can use a little less.

FAQ

What dilution ratio should I use in a pressure washer?

Most residential pressure washers use a downstream injector that pulls detergent at roughly 10 parts water to 1 part detergent, so detergent is about 1/11 of the finished solution. A siphon tube draws richer, closer to 5:1. A pre-mix bucket lets you set any ratio, commonly 10:1. This calculator gives the exact detergent and water volumes for the method you choose.

How long should I let detergent sit before rinsing?

It depends on the surface: 3 to 5 minutes for vinyl siding, decks, and fences, 1 to 3 minutes for vehicles, 5 to 10 minutes for a general patio, 10 to 15 minutes for mildewed concrete, and 15 or more minutes for driveway oil stains. The detergent does the cleaning, so never let it dry before you rinse.

Can I put bleach in my pressure washer?

No. Sodium hypochlorite (bleach) corrodes pump seals and injector valves within weeks. If a job needs bleach, apply it with a separate pump sprayer, let it dwell, then rinse with the pressure washer using water only.

Why does my detergent not seem to work?

Usually it is drying before the rinse, a too-gentle vehicle-safe formula on a tough surface, or hard water cutting its effectiveness. Hard water is common in the prairie provinces, much of Ontario, and parts of the US Midwest; soft water in BC, Atlantic Canada, and the Pacific Northwest means you can use a little less.

Bottom line

Get the dilution right for your method, match the detergent strength to the surface, and let it dwell the recommended time before rinsing with a wide tip. That, plus keeping bleach out of the machine, covers almost every residential pressure-washing job. Size the machine with the PSI and GPM Calculator and plan the job with the Cleaning Time Calculator.