A calculator for mobile valeters and detailers who carry their own water. Enter your tank, your pressure washer and how you work, and it shows how many cars a tank will wash, how much water a day needs, what the full tank weighs and how much product to load.
The usable volume. Leave a margin if your pump cannot draw the last few litres.
From the rating plate. 480 litres an hour is 8 litres a minute.
Only the time the trigger is pulled, not the whole job. Time one wash to find yours.
Buckets, pump sprayers and rinsing mitts.
For one product, for example a 1 litre foam cannon bottle. Run it again for each product you use.
1 part product to this many parts water, as on the label.
How the sums work
- Water per car = pressure washer flow in litres a minute × minutes of trigger time, plus any bucket and sprayer water.
- Cars per tank = tank size ÷ water per car, rounded down.
- Tank weight = 1 kg for every litre of water. The tank, frame, pump, hose reel and generator are on top of that.
- Product per car = mix used ÷ (ratio + 1). A ratio of 1:15 means 1 part product to 15 parts water, so a 1 litre mix holds about 62.5 ml of product.
Cars per tank at a glance
Whole cars from a full tank, for five levels of water use per car.
| Tank | 40 L a car | 60 L a car | 80 L a car | 100 L a car | 120 L a car | Water weight |
|---|---|---|---|---|---|---|
| 250 litres | 6 | 4 | 3 | 2 | 2 | 250 kg |
| 350 litres | 8 | 5 | 4 | 3 | 2 | 350 kg |
| 500 litres | 12 | 8 | 6 | 5 | 4 | 500 kg |
| 650 litres | 16 | 10 | 8 | 6 | 5 | 650 kg |
| 1000 litres | 25 | 16 | 12 | 10 | 8 | 1000 kg |
Water used by trigger time
Pressure washer water only. Add your bucket and sprayer water to get the figure per car.
| Flow | 4 minutes | 6 minutes | 8 minutes | 10 minutes |
|---|---|---|---|---|
| 6 L/min (360 L/h) | 24 L | 36 L | 48 L | 60 L |
| 7 L/min (420 L/h) | 28 L | 42 L | 56 L | 70 L |
| 8 L/min (480 L/h) | 32 L | 48 L | 64 L | 80 L |
| 9 L/min (540 L/h) | 36 L | 54 L | 72 L | 90 L |
| 10 L/min (600 L/h) | 40 L | 60 L | 80 L | 100 L |
| 11 L/min (660 L/h) | 44 L | 66 L | 88 L | 110 L |
Check the weight before you fit a bigger tank
- Water weighs 1 kg a litre, so a 500 litre tank carries half a tonne and a 1000 litre tank carries a full tonne, before any equipment.
- Your van's maximum weight is on a plate or sticker on the vehicle and in the handbook. GOV.UK explains the terms in vehicle weights explained.
- Subtract the empty weight of the van from that maximum to get the payload. Tank, water, machine, generator, products and people all have to fit inside it.
- A part filled tank surges under braking and cornering. Baffled tanks and proper fixings exist for that reason. Follow the tank maker's fitting instructions.
Getting more cars from a tank
- Shorten trigger time. It is usually the biggest number in the sum. Rinse in a set order from the top down and release the trigger between panels.
- Pre treat first. A pump sprayer of pre rinse on the lower panels uses about a litre and loosens the dirt before the pressure washer has to.
- Mix at the label ratio. A stronger mix costs more and takes longer to rinse off. Our dilution ratio calculator gives exact amounts for any container.
- Match the foam cannon to the machine. A mismatched orifice gives thin foam however much product you use. Check yours with the foam cannon orifice calculator.
Washing on customers' premises also means dealing with the run off. Our guide to washing without polluting drains and rivers covers what the rules expect of businesses.
Common questions
How many cars can I wash with a 500 litre tank?
It depends on your water use per car. At 68 litres a car, which is 6 minutes of trigger time on an 8 litres a minute machine plus 20 litres of bucket water, a 500 litre tank washes 7 cars. At 100 litres a car it washes 5.
How much does a full water tank weigh?
1 kg for every litre of water, plus the tank itself. A full 500 litre tank holds 500 kg of water and a full 1000 litre tank holds 1000 kg.
How much water does a pressure washer use per car?
Flow multiplied by trigger time. A machine rated at 480 litres an hour uses 8 litres a minute, so 6 minutes of trigger time is 48 litres. The rating plate gives the flow and a stopwatch gives the time.
How much snow foam do I need for a day of valeting?
Multiply the product in one mix by the number of cars. A 1 litre foam cannon bottle at 1:15 holds about 62.5 ml of product, so six cars need about 375 ml and a 5 litre container covers about 80 cars.
Should I put shampoo in the water tank?
No. Keep the tank as clean water for rinsing, and mix products in the foam cannon bottle, a pump sprayer or a bucket at the ratio on the label.
You are welcome to link to this calculator. Questions about trade supply? See bulk, trade and wholesale or email hello@soapx.co.uk.
