Hand Washing Duration Calculator

Hand washing is the cheapest infection control there is, and almost nobody does it properly.
The CDC (Centers for Disease Control and Prevention) and WHO (World Health Organization) both put the floor at 20 seconds of active scrubbing with soap and water.
Observational studies keep finding an average closer to 6 seconds, and a sizeable minority who skip soap entirely.

The four steps, and where the time actually goes:

1. Wet: Turn on the water and wet your hands (1 to 2 seconds)
2. Lather and scrub: This is the whole 20 seconds and more. Soap, then all surfaces: interlaced fingers, backs of hands, thumbs, fingernails, wrists
3. Rinse: Under running water (5 to 10 seconds)
4. Dry: Properly, with a clean towel or air (10 to 20 seconds)

Only step 2 is what the calculator above gives you. The 20-second figure everyone quotes is scrubbing time, not total time at the sink, which is why a “20-second” wash really takes closer to 40 seconds start to finish.

Drying is not the optional part. Wet hands transfer bacteria far more readily than dry ones, so a perfect 30-second scrub followed by a wipe on your trousers gives back much of what you gained.

Total time at the sink: roughly 40 to 90 seconds for everyday situations. The WHO puts the whole procedure at 40 to 60 seconds. A surgical scrub takes 2 to 6 minutes, and it is a different procedure rather than a longer version of this one.

The 20-second rule:

The usual trick is singing “Happy Birthday” twice, which runs about 20 seconds.
Counting works too, though people count fast when they are impatient, so a clock beats a count for anything over half a minute.
The point of the song is not the song. It is that 20 seconds feels much longer at a sink than it does in your head.

When the 20 seconds changes, and when it does not:

• Raw meat, poultry and eggs: the CDC figure is still 20 seconds. The failure is skipping it, not scrubbing too briefly. In a 2018 USDA test-kitchen study, people cooking a meal washed properly only 3% of the times they should have, and often dried on a towel they had touched with raw chicken.
• Visibly dirty or greasy hands: longer, until the dirt is gone. The extra 10 or 20 seconds the calculator adds for dirty hands is this page’s allowance, not an official figure.
• Hospitals and clinics: the same 20-second scrub, or 20 to 30 seconds of alcohol rub, which the WHO prefers between patients when hands are not visibly soiled.
• Before surgery: a 2 to 6 minute surgical scrub with an antiseptic.
• After handling chemicals or pesticides: no agency publishes a time, so the calculator doubles the scrub to 40 to 60 seconds. Check the product safety data sheet, because a corrosive splash needs a 15 to 20 minute flush instead.

Key areas often missed:

• Thumbs (most commonly missed area)
• Between fingers
• Backs of hands
• Under fingernails
• Wrists

Hand sanitizer vs. soap:

Soap and water is always preferred when hands are visibly soiled. Alcohol-based sanitizer (at least 60% alcohol) is effective for many pathogens when water is unavailable, but it does not work well against norovirus, C. difficile or Cryptosporidium, or on dirty or greasy hands.