Calculate detailing concentrate use and cost per mixed litre or gallon

The short answer

To find what a diluted detailing product costs, first work out how much ready-to-use solution the concentrate makes. Then divide the purchase price by that mixed volume. For a label ratio written as 1 part concentrate to X parts water, the mixed yield is the container volume × (X + 1). The cost per mixed litre or gallon is the price ÷ that yield. For example, a 5 L container bought for $60 and mixed at 1:19 makes 100 L of solution, which costs $0.60 per mixed litre.

Two conditions change the result. First, you need to know whether the ratio counts parts of water or parts of finished mixture. Second, every volume must be in the same unit before you calculate. The figure covers product cost only. It leaves out water, labour and equipment, and it says nothing about how well the product performs.

Terms used in the calculation

• Concentrate: the product as it comes out of the container, before any water is added.
• Dilution ratio: the proportion of concentrate to water, or of concentrate to finished mixture, given on the label for a specific job.
• Concentrate fraction (f): the share of each unit of mixed solution that is concentrate. At 1:19 concentrate to water, f is 1/20, or 5%.
• Mixed yield (Y): the total volume of ready-to-use solution one container makes.
• Cost per mixed unit: the product cost of one litre or one gallon of ready-to-use solution.

What you need before you start

• Purchase price (P) of the concentrate container, in one currency.
• Container volume (C), with its unit stated: litres, millilitres, US gallons or US fluid ounces.
• The exact dilution the manufacturer's label gives for the task you are doing, and which convention it uses.
• Optional: the mixed volume (V) you actually use for one wash or task, measured in your bucket, sprayer or foam bottle.

Many detailing concentrates list several dilutions for different jobs, such as a light maintenance wash versus heavier cleaning. Each dilution has its own cost per mixed litre, so run the calculation separately for each one. Where the label's directions differ from any general figure, follow the label.

The formulas

Concentrate fraction
  Ratio 1:X (concentrate : water)       f = 1 / (X + 1)
  Ratio 1:N (concentrate : final mix)   f = 1 / N
  Percentage of final mix               f = percent / 100

Mixed yield               Y = C / f
Cost per mixed unit       = P / Y
Concentrate per unit mix  = f

Optional, for one wash using mixed volume V:
  Concentrate used        = V × f
  Product cost            = V × P / Y

Hillyard, a cleaning chemical manufacturer, uses the same approach for cost per diluted gallon. It starts from the container volume, the purchase price and the label's dilution for that application. The yield is the container volume multiplied by one plus the parts of water, and the cost is the price divided by that yield.

Avoid the most common ratio mistake

A 1:19 ratio means 1 part concentrate plus 19 parts water, which makes 20 parts in total. The concentrate is therefore 1/20 of the mix, not 1/19. Some published examples divide the mixed volume by X alone, which leaves out the concentrate's own volume. That method overstates how much concentrate you use and understates your yield. The error is small at weak dilutions but significant at strong ones. At 1:4, for instance, the concentrate is 1/5 of the mix (20%), not 1/4 (25%).

Concentrate : water	Concentrate fraction	Mixed yield per 1 L of concentrate
1:4	1/5 (20%)	5 L
1:9	1/10 (10%)	10 L
1:19	1/20 (5%)	20 L
1:49	1/50 (2%)	50 L
1:99	1/100 (1%)	100 L

Some labels state the ratio against the finished solution instead, for example 1 part in 20 parts of final mix. In that case use f = 1/N directly. If the label does not make the convention clear, check the manufacturer's full directions or technical data before you rely on the result.

Ounces per gallon: two different conventions

US labels often give dilution as fluid ounces per gallon. Here the convention matters as much as it does for ratios, because one US gallon is 128 US fluid ounces (about 3.785 litres).

• Ounces added to a gallon of water: 4 oz plus 128 oz of water makes 132 oz of mixture, so f = 4/132 (1/33).
• Ounces contained in a finished gallon: 4 oz topped up to 128 oz in total, so f = 4/128 (1/32).

Illustrative example: a hypothetical 1 US gallon (128 fl oz) jug costs $40 and is used at 4 oz per gallon. Under the added-to-water convention it makes 33 gallons of mixture, at about $1.21 per mixed gallon. Under the finished-gallon convention it makes 32 gallons, at $1.25 per mixed gallon. Also, keep fluid ounces, which measure volume, separate from weight ounces. A product dosed by weight cannot go into this formula until you convert it using the product's density.

Convert units first

Put the container volume, the dilution and any measured consumption into one unit before calculating. Mixing millilitres of concentrate with litres of water, or US fluid ounces with litres, is the usual way a correct formula ends up giving a wrong answer.

• 1 US gallon = 128 US fluid ounces ≈ 3.785 L
• 1 L = 1,000 mL
• Cost per US gallon = cost per litre × 3.785
• Cost per litre = cost per US gallon ÷ 3.785

Worked example

This is a hypothetical calculation, not a product recommendation. A 5 L concentrate costs $60, and the label is assumed to authorise 1:19 concentrate to water for the intended task.

• 1. Concentrate fraction: f = 1 / (19 + 1) = 1/20 = 0.05.
• 2. Mixed yield: Y = 5 L ÷ 0.05 = 100 L.
• 3. Cost per mixed litre: $60 ÷ 100 L = $0.60.
• 4. Cost per mixed US gallon: $0.60 × 3.785 ≈ $2.27.
• 5. One wash using 2 L of mixed solution: 2 × 0.05 = 0.10 L (100 mL) of concentrate, costing 2 × $0.60 = $1.20 in product.

Working out consumption per wash

Per-wash cost is only as good as your measurement of V. A figure from someone else's routine won't fit your car, and there is no reliable standard volume per vehicle. Measure the mixed solution you actually use: mark your bucket or sprayer, note the level before and after, and record the difference.

Some equipment adds water after you fill it, such as a foam cannon attached to a pressure washer or an inline injector. With these, the ratio in the bottle is not the ratio that reaches the paint. In that case it is simpler to track the concentrate itself. Note how much concentrate you measured into the equipment and multiply that volume by the concentrate's price per litre (P ÷ C). Doing so gives the product cost directly, without needing the final dilution.

What the result shows, and what it doesn't

• Show the convention used (parts of water or parts of final mixture), the normalised unit, the mixed yield, the concentrate used per wash and the product-only cost.
• Use the result to compare containers of the same product, or different products at their authorised dilutions for the same job.
• A lower cost per mixed litre does not mean equal cleaning ability, lubricity or surface safety. Diluting beyond the label to cut cost changes the product's intended use.
• The figure leaves out water, electricity, towels, equipment wear, labour and any service pricing.