The cap is not a measuring cup
Almost every laundry problem people blame on their machine — stiff towels, grey whites, a musty smell in the drum — starts with too much detergent. Caps are moulded larger than the recommended dose, and the fill lines are often invisible against white plastic. A modern high-efficiency machine uses roughly half the water of a 1990s top loader, so the dose that made sense on the old bottle now leaves suds the rinse cycle cannot clear.
Start with your water hardness
Hard water binds the surfactants in detergent before they reach your clothes, which is why the same bottle cleans beautifully in one city and poorly in another. If your kettle scales up within a month, you have hard water and genuinely need the upper end of the dose range — or better, a dose of washing soda alongside a normal amount of detergent. In soft-water regions, most households can drop to two thirds of the labelled dose with no visible difference. Your water utility publishes hardness in grains per gallon or parts per million; it takes two minutes to look up and it settles the question permanently.
Dose by soil level, not by drum size
A full drum of lightly worn office shirts is far less soiled than a half drum of gym kit and toddler clothes. Detergent works on soil, not on volume. Use the labelled dose for genuinely dirty loads — sports, garden work, kitchen aprons, anything with body oils — and cut it by a third for the refresh loads that make up most of a normal week. Bedding and towels sit in the middle: they hold body oil but little visible dirt.
Pods are a fixed dose, so match the load to them
Single-dose pacs remove the guesswork but also remove the flexibility. One pac is calibrated for a normal, full, medium-soil load in average water. Do not add a second pac to a big load of towels unless the packaging explicitly allows it, and never cut a pod open to split it — the film is designed to dissolve as a unit, and a half dose of concentrated enzyme paste tends to smear rather than disperse. Drop the pac into the empty drum before the clothes, never into the dispenser drawer, where it can stick and only partly dissolve.
How to tell you are overdosing
Four reliable signs: towels that feel stiff and stop absorbing, dark cotton that develops a chalky cast after a dozen washes, a sour smell from the door seal or dispenser, and visible suds still clinging to the glass at the end of the final rinse. Any one of these means detergent is being left behind in fibres and machine parts, where it holds soil and feeds bacteria. The fix is not a stronger product — it is a smaller dose plus one hot maintenance wash with the drum empty.
A dosing routine you can keep
Buy a cheap 30ml measuring cup and keep it with the detergent so you stop pouring by eye. Write your standard dose on the bottle with a marker. For a fortnight, run everyday loads at two thirds of the label amount and watch for anything coming out less clean — in most homes nothing changes except softer towels and a bottle that lasts a third longer. If a specific load does come out dull, raise the dose for that load type only rather than resetting the whole routine.