Methods and sources
Where each tool’s answer comes from, and how far it has got.
| Tool | Where the answer comes from | Right now |
|---|---|---|
| Child height percentile calculator | The chosen standard’s LMS parameters turn the height into a z-score, then a percentile. | Against a reference |
| Height growth calculator | Later minus earlier; dates subtracted on the calendar. No health threshold is involved. | Computes |
| Growth chart maker | Your own dates and values, spaced by date. No reference bands underneath. | Computes |
| Height percentile to centimetres | The same LMS parameters as the forward calculator, solved the other way round. | Against a reference |
| Child weight percentile calculator | The chosen standard’s LMS parameters turn the weight into a z-score, then a percentile. | Against a reference |
| Weight change calculator | Units matched, then later minus earlier; dates subtracted on the calendar. | Computes |
| Child BMI calculator | Weight in kilograms divided by height in metres squared. The placing comes from a BMI-for-age table. | Against a reference |
| Visual acuity notation converter | Decimal = 1 ÷ minimum angle of resolution. Three scales for one quantity, so conversion is arithmetic. | Computes |
| Screen and outdoor time reference | Published guidance retrieved by age and source, keeping each source’s own definition of the time. | Against a reference |
| Tooth eruption timing | The source table’s eruption age range, retrieved by tooth type and position. | Against a reference |
| Children’s sleep duration reference | Published guidance retrieved by age and source, keeping each source’s own basis for the figure. | Against a reference |
| Sleep duration calculator | Time in bed, minus minutes awake in the night, plus that day’s nap. | Computes |
| Nutrient reference intake lookup | Reference intakes retrieved by age, sex and nutrient, keeping the source’s value type and unit. | Against a reference |
| Feeding and diet reference | Published guidance retrieved by source, age and topic, keeping the original units and scope. | Against a reference |
| Nutrition label intake calculator | Label amount × portion eaten ÷ the label’s reference amount. | Computes |
What a lookup by age is actually read against
Seven regions, twelve tables. Pick a region and the answer comes from that region’s tables; at the same age two regions often give different numbers, and that is not an error.
| Region | Standard | Height covers |
|---|---|---|
| Chinese mainlandNational Health Commission of China (国家卫生健康委员会) |
| to 18 years |
| Hong Kong SARDepartment of Health (衞生署), with CUHK and HKU |
| to 18 years |
| JapanChildren and Families Agency (こども家庭庁), formerly the Ministry of Health, Labour and Welfare |
| to 19 years |
| Republic of KoreaKorea Disease Control and Prevention Agency (질병관리청), with the Korean Pediatric Society |
| to 19 years |
| United KingdomRoyal College of Paediatrics and Child Health (RCPCH) |
| to 20 years |
| United StatesCenters for Disease Control and Prevention (CDC) |
| to 20 years |
| World Health OrganizationWorld Health Organization |
| to 19 years |
Sources are chosen by question, not by language.
Tools with a regional reference name the region, the version, the ages covered and how the measurement was defined. Reading the site in another language does not change the reference — those are two different things. Where coverage runs out, it says so.