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What is the best way to determine how much detergent to use to clean my clothes in any average washing machine.

Some of the suggested guidelines I've come across are:

The published (detergent manufacturer's suggested) method is to measure for a normal load to the slightly raised line molded into the cap for the detergent container (by volume). For a heavy (dirty) load, fill to the second mark molded into the cap.

The published (washer manufacturer's suggested) method is to load the washer tub loosely to a mark on the agitator after you have added the detergent (determined by the above) to the empty washer tup before loading.

Fine.

Often, people have gotten on the bus or into a subway car and the strong odour of their clothing fills the car within seconds of their arrival. They reek of the detergent. Evidently, the existing odour from an excessive amount of the detergent is associated with 'clean' as opposed to chemically 'contaminated.' The brand, notwithstanding. Just sayin'

When I wash my clothes, I need enough detergent/soap to get the dirt out of my clothes; but, without using an excess which is wasteful and environmentally destructive.
How can I determine the correct/optimal amount of detergent to use in any situation given that the optimal amount is affected by:

  • The wash load weight
  • The load volume
  • The kind of fabric
  • The amount and kind of 'dirt' in the fabric
  • The water hardness/softness
  • The water temperature
  • The concentration of the detergent
  • The washing machine itself?

After the dirty-work is done, I want the wash water to take the suspended material away in the rinse which under expected conditions should be part of normal operation for the make and model.

Summary: Long story short: I want to determine the minimum effective detergent concentration during the wash cycle, in real time, not after the fact.

Hint: If one added excessive detergent, say, what would indicate such an oversight before the wash cycle is complete?
If one forgot to add detergent, what would indicate such an oversight before the wash cycle is complete?
— Somewhere between those two extremes is the answer. It should not matter if sweatpants used in mud wrestling is in one load and an equivalent weight of grand-mother's crochet table runners is in the next.

Is there a lifehack?

Thank you.

  • Have you noticed an excessive detergent odour on clothes you've washed? Are you suspicious manufacturer's recommendations are incorrect? – Hobbes Jul 14 at 12:31
  • Hi, @Hobbes There are many variables, few indications, one desired outcome, and no definitive answer. My personal interest is in evangelizing pollution reduction and Multiple Chemical Sensitivity awareness. YES. I am also skeptical of the motives behind multi-national corporate marketing recommendations. – Stan Jul 14 at 14:03
  • It's not really something you life hack though, so it seems a bit off topic for the site? You've correctly identified a considerable number of variables to the problem and you're now well on the way to doing with your washing what car makers continue to do with ECUs when they got rid of wasteful carburettors - the car runs a fuel map with constant analysis of the environment and exhaust composition- you might just have to invent the same thing for the washer! – Caius Jard Jul 17 at 12:53
  • I understand. I cannot comment about those who do not care. Newspaper headlines feature these care free individuals and their carelessness every day. The same could be said about every question on Lifehacks. I'm looking for a simple solution (chuckle, chuckle) to a daily 'health' (ultimately) issue. @CaiusJard – Stan Jul 19 at 18:46
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This will get you in the ballpark:

  1. Use a graduated cylinder to measure how much detergent is in the manufacturer's recommendation.

  2. wash one load of clothing, of the maximum weight allowed in your machine, and with an average level of dirt, using the manufacturer's recommendation.
    A full load means the machine works most efficiently, and makes the process more repeatable.

  3. Wash the next load using 90% of the manufacturer's recommendation. After washing, check if the clothes are sufficiently clean (no visible stains or weird smells).

Repeat step 3 on subsequent loads, reducing the amount by 10% each time until it fails your check. That gives you a minimum amount of detergent to use. This process necessarily ignores some factors (exact level and type of dirt, type of fabric), but it's as close as you'll get without an exhaustive analysis of each load. That would require a chemical laboratory and a day of analysis for each load of laundry, which is clearly inefficient.

To minimize the smell, use non-perfumed detergent or choose a brand that's hypoallergenic.

There are washing machines that can do this for you during one cycle, instead of having to check the result afterwards.

They use a combination of inputs:

  • the amount of laundry (several ways to do this, either load cells to measure the weight directly, or it may be possible to do torque sensing on the motor and derive the weight from that)
  • turbidity sensor in the drain, this measures how much dirt ends up in the drain

They use these inputs to adjust not only the amount of detergent, but the entire washing cycle. Replicating this functionality is not a life hack, it'd be a major electronics and software development project, replacing half the parts in the machine.

To add these to a machine that doesn't have them, you'd need to replace the machine's computer, replicate its programming, and modify it to use the new sensor inputs. You'd have to figure out how the sensors work (e.g. what sensor reading corresponds to which level of dirt) and how this should modify the machine's program. An advanced electronics hobbyist would take months to implement this.

Or you can spend a few hundred dollars more on your next washing machine.

They reek of the detergent.

I suspect those people just dump a load of detergent into the washer rather than follow the manufacturer's specification, and end up using far more detergent than necessary. They don't need a life hack, they need to RTFM and follow the instructions therein.

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  • Thank you. That's good. Q: How could/would one determine "sufficiently clean" for example. Manufacturers recommend separating colours for washing so light and dark would be a complication to deal with too. There must be a better all-inclusive way to determine the amount to use. – Stan Jul 14 at 20:22
  • This falls short of an acceptable answer due to the shortcomings you mention. The answer applies after the fact rather than during the washing cycle so that some action can be taken. "Ballpark" is the vague answer I don't accept. BTW, measuring a viscous fluid into a graduated cylinder or getting it out consistently and conveniently would also be rather impractical. +1 for the experimental rigour. : ) I want to determine the minimum effective detergent concentration during the wash cycle, in real time, not after the fact. – Stan Jul 16 at 23:32
  • You mention the use of a graduated cylinder to measure the "stuff." I would think that this would include various other kinds of "dispensers" to deliver known amounts per application, like a pump. The precise amount would then be known from load to load. This would be handy if the loads were all the same or very similar. The automatic dispensers (as in your link) built-in some washers perform a similar function. They do not "measure the amount of dirt" beyond your settings when you load the washer. Being able to specify the amount that was used is less important than the effective amount used. – Stan Jul 19 at 0:20
  • There should be a method to accomplish what I wish to do without modifying any hardware whatsoever. I believe it involves a simple lifehack in the purest sense. The precise amount of detergent for one load does not affect the precise amount used for another. You are headed in the wrong direction according to experts. What do they know that would answer my question? Note that I mentioned any average washing machine. Thank you all the same for your effort. – Stan Jul 19 at 18:50
  • I don't believe such a method exists, other than to follow the detergent manufacturer's recommendation. If you have found experts saying otherwise, write an answer with links to those experts. – Hobbes Jul 19 at 19:33
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The Science: Soaps and detergents are made from long molecules that contain a head and tail. These molecules are called surfactants. The head of the molecule is attracted to water (hydrophilic) and the tail is attracted to grease and dirt (hydrophobic).

The Problem: There is no average recommended amount of detergent—no universal mark on the cap. The manufacturer cannot account for all the variables in your wash load. All things being considered, the optimal amount of detergent is the amount that is required to remove the grease and dirt from your laundry—and no more.

The Answer: The optimal amount must be determined by your kind of wash load each and every time.

The Hack: Watch for soap bubbles. A tiny excess amount of detergent produces soap bubbles during agitation after the tub is filled. (This passed on to me from a 'detergent engineer.'

The How: After the tub has filled, add a minimum amount of detergent to the wash and let it mix thoroughly with agitation for a moment or two. Any soap bubbles? Add a tiny bit more waiting until mixed thoroughly before you check again for bubbles Use a pump-dispenser for convenience. Stop as soon as you see a few bubbles. That's it for that load. The amount of detergent will vary from load to load due to your particular circumstances for that load.

The Given: The only consideration is that the washer is not overloaded preventing proper agitation and that the washer is otherwise working properly which is a reasonable assumption.

Good luck.

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  • I am not sure whether this is convenient for front-loading machines? – Stephie Jul 25 at 9:31

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