Calculate shampoo dose from the water you actually use, then calculate cost from that dose and the bottle price you pay. Do not compare bottles by price per litre alone: two concentrates can require different amounts for the same wash volume.
The calculator below starts with a manufacturer-verified example: Autoglym Ceramic Wash & Protect specifies 30ml in 10 litres of water, and the selected bottle contains 1,000ml. Change the dose if you use a different shampoo. Entered prices and worked examples are not live Amazon offers.
Read the instruction before reaching for a measuring cup
First identify the exact product and its intended use. Bucket shampoo, pre-wash, foam-lance mixture and waterless cleaner can all have different instructions. A bottle-mixing ratio for a lance is not the same as the concentration that reaches the car after the washer adds water.
For a bucket wash, look for an amount such as millilitres per specified water volume. If the label gives capfuls, use that product’s cap instruction. Do not assume every cap holds 10ml or convert an unspecified capful using an internet rule for another brand.
Measure water into the wash bucket. Its maximum capacity is not the quantity used: 8 litres in a 20-litre bucket is still an 8-litre mix. The second bucket in the two-bucket method is plain rinse water and does not receive another dose of shampoo.
Calculate your dose and shampoo cost
The calculator estimates complete doses from the stated bottle volume. Spills, unmeasured top-ups and product left in the bottle can reduce real yield. It does not assess whether a concentration suits your paint or whether an unusually small wash volume is practical for the job.
The dose formula
When the label provides a dose per 10 litres:
Shampoo needed in ml = label dose × water litres ÷ 10.
For the verified 30ml-per-10-litre instruction, 8 litres needs 24ml, 10 litres needs 30ml and 20 litres needs 60ml. These examples change the water volume while keeping the same intended concentration. They are not recommendations to use 20 litres for every car.
| Water in the wash bucket | Shampoo amount | Complete doses from 1,000ml |
|---|---|---|
| 8 litres | 24ml | 41 |
| 10 litres | 30ml | 33 |
| 15 litres | 45ml | 22 |
| 20 litres | 60ml | 16 |
The complete-dose figure is rounded down. With a 30ml dose, 33 washes use 990ml and leave a theoretical 10ml. That remainder is not another complete wash dose. Keep the bottle’s label intact rather than using the calculation to justify a weaker final mixture.
A product with a published measured dose
The Ceramic Wash & Protect example is useful because both dose and bottle size are explicit. It is still a finishing choice, not the automatic best-value shampoo for every car. Its gloss-enhancing film and matt-paint exclusion may make a different product more appropriate.
For a wash with added finishing film
Autoglym Ceramic Wash & Protect 1L
A low-foaming shampoo that adds a water-repellent, high-gloss finish. The manufacturer gives a measurable dose of 30ml per 10 litres, making bottle-yield calculations straightforward.
- 1 litre concentrate
- 30ml per 10 litres
- Added protective film
Not recommended for matt paint. Check your coating’s maintenance guidance and follow the exact label. Autoglym recommends cleaning the windscreen afterwards with a suitable glass product.
Work out cost per wash
Shampoo cost per wash = bottle price × dose in ml ÷ bottle volume in ml.
For a purely illustrative bottle price of £12, a 1,000ml bottle used at 30ml per wash costs £0.36 in shampoo per wash. The £12 is a hypothetical input, not an advertised price for the linked product. If the price you pay is different, replace it in the calculator.
For 8 litres of wash water at the same concentration, the 24ml dose would cost £0.288 at that hypothetical bottle price, or about 29p when rounded to the nearest penny. It is useful to keep the calculation unrounded until the final display.
Include delivery in your entered bottle price if you want that cost allocated across washes. The tool does not add it automatically. Water, electricity, towels, wheel cleaner and finishing products are separate costs, so this is not a total price for cleaning the car.
Compare published doses on the same basis
A smaller bottle can supply more wash solution when its stated dose is lower. To make that visible, we calculated the dose for a common 10-litre mix and the number of complete mixes from two selected bottle sizes. GWash has separate light- and heavy-dirt instructions, so both appear below. For GWash, this model assumes 23 litres of water in the maker’s stated 23-litre bucket. Bucket capacity and the water actually added can differ; the GWash results change if that assumed fill changes.
| Bottle and instruction | Published dose | Calculated dose for 10 litres | Complete 10-litre mixes |
|---|---|---|---|
| Ceramic Wash & Protect 1L Published bucket dose | 30ml in 10 litres of water | 30ml | 33 |
| GWash 500ml Light-dirt instruction | 20ml for a 23-litre bucket | 8.7ml | 57 |
| GWash 500ml Heavy-dirt instruction | 40ml for a 23-litre bucket | 17.39ml | 28 |
Under the 23-litre fill assumption, the 500ml GWash bottle gives 57 complete 10-litre mixes at the light-dirt rate, compared with 33 from the 1-litre Ceramic Wash & Protect bottle. At GWash’s heavy-dirt rate it gives 28. The instruction you actually need changes the buying calculation; bottle size alone cannot settle it.
Use the appropriate dirt-level instruction rather than choosing a weaker mix to improve the figures. These are different finishing choices: Ceramic Wash & Protect adds a protective film, while GWash is a maintenance shampoo. Check the car’s finish and the exact bottle instructions before comparing costs.
Where the inputs come from
- Autoglym’s UK page identifies the 1-litre pack and gives 30ml in 10 litres.
- Gtechniq’s UK page lists a 500ml option and gives 20ml for light dirt or 40ml for heavy dirt in a 23-litre bucket. The analysis treats that nominal bucket size as a 23-litre water fill; it does not establish how much water you actually put in your bucket.
Method: dose for the comparison = published dose × 10 ÷ the model’s water litres. Complete mixes = bottle volume ÷ that unrounded dose, rounded down. Displayed doses use up to two decimal places; the calculation keeps the unrounded value. Scaling to 10 litres is an arithmetic comparison, not a new product instruction.
One mix is not automatically one complete car wash. Top-ups, spills and residue reduce practical yield, and the rinse bucket is separate. Foaming Car Wash remains outside this numeric comparison because its cited instruction gives capfuls without a verified millilitre quantity.
Download the calculation data and source links (CSV). Input and calculated columns are labelled separately. The CSV keeps up to 12 significant digits for calculated values; use the source inputs to reproduce the comparison or replace the amounts with those on your pack.
Work out the price that makes the doses equal
Once both products suit the job, compare what each 10-litre mix costs. These thresholds retain the GWash 23-litre water-fill assumption above. The GWash 500ml bottle reaches the same shampoo cost per mix as the Ceramic Wash & Protect 1-litre bottle at the following price thresholds:
| GWash instruction | GWash bottle price at equal cost | If the Ceramic bottle cost £12 |
|---|---|---|
| Light-dirt instruction | 172.5% of the Ceramic bottle price | £20.70 |
| Heavy-dirt instruction | 86.25% of the Ceramic bottle price | £10.35 |
The £12 is the same hypothetical price used in the example above, not an Amazon offer. Below the threshold, GWash has a lower allocated shampoo cost for the stated mix; above it, Ceramic Wash & Protect does. Compare the finishing role separately. The thresholds use the full-precision dose, not the rounded-down count of complete mixes.
Threshold formula: Ceramic bottle price × (GWash bottle ml × Ceramic dose per 10 litres) ÷ (Ceramic bottle ml × GWash dose per 10 litres). Include delivery consistently in the bottle prices you compare. Water, electricity, tools and any separate finishing product remain outside the calculation.
A standalone bucket-wash shampoo
Gtechniq GWash 500ml
A concentrated, pH-neutral shampoo for a regular contact wash. A useful single-bottle choice when you already own a mitt and towels and do not need another boxed set.
- 500ml concentrate
- Bucket-wash shampoo
- pH-neutral formulation
Use the dilution on your UK bottle. This is GWash, not Ceramic GWash or a snow-foam pre-wash; follow your coating or finish supplier’s care instructions.
Compare two shampoos fairly
When a bundle is involved, compare the complete boxed or separate kit as well as shampoo consumption. A cheap dose is useful only if the purchase also fits the equipment and finishing routine you need.
Use the same practical wash-water volume for both products and each one’s own label dose. Then compare the wash-stage job each covers. A shampoo with an added finishing film is not identical to a clean-rinsing wash, even if their cost per dose is similar.
Do not assume a stronger concentrate cleans better because it uses fewer millilitres, or a large bottle is cheaper because it contains more liquid. Use the calculation to compare buying costs after checking compatibility and the finishing role you want.
What if the dose is only given in capfuls?
Autoglym Foaming Car Wash specifies two capfuls in 10 litres. Follow the exact bottle instruction rather than assigning an unverified millilitre value to its cap. If you want a precise cost comparison, obtain the manufacturer’s verified volume or measure the actual cap accurately using a dedicated suitable measuring vessel.
For a clean-rinsing bucket wash
Autoglym Foaming Car Wash 1L
A pH-neutral shampoo without added finishing film. The 1-litre bottle is a separate purchase when you already own your wash tools or prefer a separate wax or sealant step.
- 1 litre concentrate
- No added finishing film
- Two capfuls per 10 litres
Autoglym specifies two capfuls in 10 litres of water. Keep panels cool, rinse thoroughly and do not let the solution dry. Check the label and safety data sheet for your pack.
Avoid the common ratio mistakes
A direction of “one part product to ten parts water” means eleven parts total. A direction of “one part in ten total” is different. Check the wording before doing arithmetic, and ask the manufacturer when the label is ambiguous.
Keep units consistent. Convert litres of bottle contents to millilitres before dividing by a millilitre dose; 1 litre is 1,000ml. Do not mix UK and US gallon assumptions or borrow a dilution from another country’s formulation.
Use a dedicated measuring tool and keep it out of food preparation. Rinse it according to the chemical and equipment instructions, and keep all products in identifiable containers. Wear the protective equipment specified on the product label or safety sheet.
If the wash feels wrong, check the setup
Do not add concentrate simply because there is less foam than expected. Some shampoos are low foaming by design. Excess solution drying on warm paint, dirty rinse water or an unclean mitt can make a wash difficult even when the bottle itself is suitable.
Check the label, measured water volume and tool condition first. Then use the shampoo comparison if you need a different finishing behaviour, or the washing routine if the problem is sequencing rather than quantity.
Common questions
How much shampoo goes in a 10-litre bucket?
Use the amount stated for the actual product. The worked example is 30ml of Autoglym Ceramic Wash & Protect in 10 litres. Autoglym Foaming Car Wash instead gives a capful instruction. Neither amount should be transferred to another shampoo without checking its label.
Should I fill a 20-litre bucket to the top?
Not necessarily. Bucket capacity and the amount used are different. Measure a practical volume with room for the tool and hand, then dose for that water amount. Avoid filling so high that rinsing the mitt repeatedly spills the mixture.
Why does the calculator round the wash count down?
It reports complete doses. A 1,000ml bottle at 30ml per wash contains 33 complete doses with 10ml theoretically remaining. A fractional result is useful arithmetic but does not mean the remainder provides another correctly dosed wash.
Does a smaller shampoo bottle always cost more per wash?
No. Compare the bottle price, usable volume and the dose for the same water quantity. The published-dose comparison gives separate GWash light- and heavy-dirt cases because the chosen instruction changes the result. Check the finishing role and compatibility before comparing the calculated costs.
Can I use this calculator for a snow-foam lance?
Not as a panel-concentration calculator. A foam lance introduces additional water through the washer, so the bottle mixture alone does not establish the final dilution. Follow the exact chemical and equipment method rather than applying the bucket formula to the car’s surface.
Sources and product instructions
Follow the label and care instructions for the exact version and surface you own.