Dilution Ratios and Ounces per Gallon Card

Why this matters

A concentrate is only as good as the person pouring it. Pour too little and a disinfectant loses the kill claim on its label; pour too much and a floor turns sticky, glass streaks, a stone counter dulls, and the shop burns through product at two or three times the planned rate. Most mixing errors are not carelessness. They come from not knowing how a ratio on the label turns into ounces in a bucket or a quart bottle, so the tech guesses and adds "a little extra to be safe." This card owns that conversion. Labeling the bottle once it is mixed belongs to 'Dilution Control and Labeling Standard'.

The convention this library uses

Labels state dilution two ways, and they are not always the same thing.

• Ounces per gallon means ounces of concentrate added to one gallon of water. One US gallon is 128 fluid ounces.
• A ratio like 1:64 in this library means 1 part concentrate to 64 parts water. So ounces per gallon equals 128 divided by the second number.

Some manufacturers write ratios as parts of the finished solution instead (1 part in 64 total). At high dilutions the two readings differ by a percent or two and nobody can measure the difference. At low dilutions they diverge: 1:4 read as "1 part to 4 water" is 32 ounces of concentrate into a gallon of water, while "1 part in 4 total" is 32 ounces of concentrate plus 96 ounces of water. When a label gives both a ratio and ounces per gallon, mix to the ounces per gallon, because that figure cannot be read two ways. When it gives only a strong ratio (1:10 or lower), read the label's own wording for which convention it uses.

The card

Tape this inside the van door and on the wall over the mixing station.

DILUTION CARD          1 US gallon = 128 oz
RATIO   OZ PER GALLON   OZ PER 32 OZ BOTTLE
1:16         8              2
1:32         4              1
1:64         2              1/2   (1 tbsp)
1:128        1              1/4   (1 1/2 tsp)
1:256        1/2            1/8   (3/4 tsp)
--------------------------------------------
oz per gallon = 128 / N
oz per bottle = 32 / N
2 tbsp = 1 oz      1 tbsp = 3 tsp
label in oz/gal -> ratio N = 128 / oz

Two checks that the card is right, worked the other way: 2 ounces per gallon gives 128 divided by 2, which is 64, so 1:64; and half an ounce in a 32 ounce bottle gives 32 divided by 0.5, which is 64 again. Every row closes in both directions.

The bottle column treats the 32 ounces as water. In practice you add the concentrate first, then fill to the shoulder, which leaves slightly less water than 32 ounces. At 1:64 that error is under 2 percent; at 1:16, 2 ounces of concentrate in a 32 ounce bottle filled to the top works out nearer 1:15. Neither matters for a cleaner. For a disinfectant mixed at 1:16 or stronger, measure both volumes rather than filling to the shoulder.

Add concentrate to water, not water to concentrate, for anything corrosive. Pouring water onto a strong acid or caustic can spatter concentrate at the person pouring; pouring concentrate into water dilutes it as it goes. Goggles and gloves at the mixing station are whatever the label's precautionary statements require, and for a corrosive concentrate that is goggles, not glasses.

Bigger containers, same arithmetic

Measure the water too. A "two-and-a-half gallon" fill in a mop bucket is often closer to three gallons once someone fills it to the line they are used to, and a 20 percent error in the water is a 20 percent error in the dilution. Mark the fill line on the bucket in permanent marker after measuring it once with a gallon jug.

Proportioners and wall dispensers do this for you by drawing concentrate through a metering tip sized for one ratio. The tip, the water pressure and the hose condition all matter, so check one: dispense a measured gallon, note how much the concentrate jug dropped (a graduated cup under the pickup tube for one fill does it), and compare against the card. A tip that has been swapped, or a cracked pickup line drawing air, shows up the first time anyone checks.

Odd bottles and metric labels

The formula works for any container: ounces of concentrate equals the container's water volume in ounces divided by N.

• A 24 ounce bottle at 1:64 takes 24 divided by 64, which is 0.375 ounce, a little over 2 teaspoons (0.375 times 6 teaspoons per ounce is 2.25 teaspoons).
• A 16 ounce bottle at 1:32 takes 16 divided by 32, half an ounce, which is 1 tablespoon.
• A label written in milliliters per liter converts the same way with 1,000 in place of 128: 1:64 is 1,000 divided by 64, about 15.6 mL per liter. A US quart is about 0.95 liter, so a 32 ounce bottle and a 1 liter bottle are close enough that one cup mark serves both at 1:64 or weaker.
• One fluid ounce is about 29.6 mL. If a measuring cup is marked only in milliliters, 2 ounces is about 59 mL and half an ounce about 15 mL.

Ready-to-use (RTU) products are already diluted. Watering an RTU down to stretch it is the most common way a disinfectant loses its claim on a job, because nobody thinks of it as mixing.

A measuring cup beats a cap. Jug caps vary from about half an ounce to over an ounce depending on the maker, and a "capful" that was right for last year's jug is wrong for this year's. If the shop uses caps as a measure, the lead measures that specific cap once and writes its volume on the jug.

Why stronger is not better

Residue. Surfactants and quats that are not used up by soil stay on the surface. On a floor, that film is tacky and grabs the next soil that lands on it, so an overmixed floor looks dirtier a week later than a correctly mixed one. On glass and stainless, excess shows as streaks that need a second pass. On a sealed stone or a finished floor, a heavy residue dulls the shine and gets blamed on the finish.

Surface damage. An acid descaler mixed strong etches faster; a degreaser mixed strong lifts paint and dulls floor finish. Because pH is logarithmic, doubling the concentrate does not double the harshness in a linear way, but it moves the solution toward the edge of what a surface tolerates. See related: The pH Scale for Cleaning Crews: Which Chemistry Lifts Which Soil.

Rinse labor. A cleaner mixed at three times label strength usually needs a rinse the label never asked for. That is a second pass with clean water on every surface, which on a commercial restroom roughly doubles the fixture time.

Product spend. Concentrate spend scales directly with the mix. A tech pouring at three times label strength uses three times the concentrate, so a jug planned to last a month lasts about ten days.

Disinfectants are a different category. A disinfectant's dilution is part of its registration. Under FIFRA, mixing it stronger than the label is use inconsistent with the labeling, and it can push the in-use solution past what the label's PPE was written for. Mixing it weaker is carved out of that definition unless the label forbids it, but it voids the kill claim, so a log that says "disinfected" is no longer true. Neither is a judgment call. Reading the rate off the jug belongs to 'Reading an EPA-Registered Disinfectant Label', and checking a mixed quat with a test strip belongs to 'How to Mix Quat Disinfectant and Check It with a Test Strip'.

Worked example: the sticky lobby floor

An office account complains that the vinyl lobby floor feels tacky and looks gray in the traffic lanes two days after every clean. The night tech mops it with a neutral floor cleaner whose label reads 1 ounce per gallon.

What the tech was doing. Asked to show the mix, the tech fills the mop bucket "to about here" and pours "a good glug." The lead measures both. The fill line holds 2 gallons, which is 256 ounces. The glug, poured into a measuring cup, is 6 ounces.

The arithmetic. The label wants 1 ounce per gallon, so 2 gallons needs 2 ounces. The tech is pouring 6 ounces, which is 6 divided by 2, three times label strength. As a ratio: 256 ounces of water divided by 6 ounces of concentrate is about 1:43, against a label of 1:128. Checking the other way: 128 divided by 43 is about 3 ounces per gallon, and 3 ounces per gallon times 2 gallons is 6 ounces. It closes.

Why the floor looked worse. Three times the surfactant, no rinse, a floor finish that holds the film. The residue grabs grit from the parking lot and the lanes go gray within two days, which is the complaint.

The fix, in order.

1. One rinse pass with clean water and a fresh mop head on the whole lobby, to lift the built-up film, then a second if the floor still feels tacky under a clean dry palm.
2. The bucket's 2-gallon line marked in permanent marker.
3. A 2-ounce measuring cup tied to the bucket handle, and the card taped on the janitor closet wall.
4. A check after one week: the lead runs a clean white cloth across a traffic lane. Before the fix it came up gray; after, it comes up close to clean.

What changes the answer. If the label had read 1:128 with no ounces-per-gallon figure, the result is the same, because 128 divided by 128 is 1 ounce per gallon. If the floor were a natural stone lobby instead of vinyl, the overmix would also raise the question of whether the "neutral" cleaner was neutral at that strength; the stone card governs and the hidden-spot test comes first.

How to know the crew is mixing right

Spot-check one bottle and one bucket per tech per month. Pour the bottle's solution into a measuring cup to confirm the volume, ask how much concentrate went in, and compare against the card. For quat disinfectants the test strip gives an independent reading. The figure that matters is not the reading on one day but whether two techs mixing the same product get the same answer.

References

• Product labels for each concentrate the shop stocks (the dilution rate in Directions for Use governs)
• FIFRA, use inconsistent with labeling: definition at 7 U.S.C. 136(ee), unlawful act at 7 U.S.C. 136j
• See related: Dilution Control and Labeling Standard; Reading an EPA-Registered Disinfectant Label
• See related: How to Mix Quat Disinfectant and Check It with a Test Strip; Common Cleaning Chemicals Reference