Body circumferences reflect internal (visceral, paravertebral and intermuscular) and subcutaneous adipose tissue, but are also influenced by variation in lean and bone masses. The inference made from a measure of circumference varies by anatomical site:
Measures of circumference can also be combined:
Different measurement tapes are available to measure circumferences. Typically a non-stretch (e.g. fibreglass or plastic), flat, flexible, ergonomic, measuring tape is used (see Figure 1 for examples).
Precision is generally improved by using a tape that maintains a fixed tension with spring attachments or else contains a tension indicator, since this minimises intra- and inter-observer variation in the extent to which the tape is pressed onto the participant during measurement.
Figure 1 Examples of tape measures (D-loop and tape measure with spring attachment).
Source: MRC Epidemiology Unit
The instrument needs to be calibrated using a standardised one-metre rod, especially when using plastic coated fabric measurement tapes as they may stretch with use overtime introducing error. It is common practice to carry out calibration procedures on a monthly basis.
Procedure for upper arm
Procedure for chest
Figure 2 Chest – tape placed at the level of the middle of the sternum (breastbone).
Source: MRC Epidemiology Unit.
Procedure for mid-thigh
Procedure for calf
Procedure for neck
Procedure for waist
The site of WC measurement varies by study group as to date no consensus has been agreed on an optimal location. All measurements are taken along the horizontal plane, parallel to the floor. Whichever site is chosen should be used consistently for all measurements in any single study or survey group.
The most commonly used sites are:
All sites are highly reproducible even though the waist values themselves may differ greatly from site to site (Source ). Differences in measurements protocols across studies could be responsible for variation in the association of these measures with risk factors, or disease or mortality outcomes.
This presents a particular challenge for anyone attempting to harmonise waist circumference data from multiple studies obtained from different anatomical sites. It also emphasises the need for rigorous standardisation of methods in multi-centre studies or surveys, since use of multiple sites will introduce measurement error.
The protocols with the bony land marks are preferable to the soft tissue landmark, such as the umbilicus, as many individuals with obesity may present pendulous abdominal adipose panniculus (dense layers of subcutaneous fat tissue in the lower part of the abdomen), resulting in the umbilicus to be located well below the waist level. The panniculus may also interfere with the hip measurement as the waist and hip circumferences overlap.
Figure 3 Waist – midpoint between subcostal and suprailiac landmarks according to the World Health Organization (WHO) protocol.
Source: MRC Epidemiology Unit.
Procedure for hip
Figure 4 Hip – tape placed on the greater trochanter (bony projection on the side of the femur).
Source: MRC Epidemiology Unit.
Circumferences are commonly used in a variety of health related studies and in large scale epidemiological studies to assess central adiposity and fat distribution as they correlate with metabolic markers and imaging techniques estimates.
Waist circumference and BMI measurements are highly correlated with each other, at least in children above the age 5 years (R2 = 56% at 3.5 y; R2 = 61% at 4 y; R2 = 66% at 5 y; R2 = 75% at 7 y; R2 = 79% at 8 y; source: Avon Longitudinal Study of Parents and Children).
In clinical practice, this circumference would not add much to BMI to distinguish which children are overweight. However, at younger age groups, waist measurement may potentially provide additional information beyond BMI.
In research settings, simple measures like waist and hip other than BMI and weight may help understanding the causes of adiposity and assess intervention with longer term benefits.
Measurements should be quality checked during data processing in the same manner as other health related variables, for example by checking for outliers and data entry errors. It is recommended to use valid ranges for these circumferences according to the study population (e.g. children, adults etc.) when building the study database.
There are no specific steps, which are unique to these measurements. In some circumstances, it may be necessary to convert units taken in imperial units (inches) to metric units (cm).
Circumference ratio indices
Circumferences are often used in combination with each other or with other anthropometric measurements such as height, to calculate anthropometric ratio indices. This requires the division of two numbers (e.g. 2 circumferences or one circumference and one other anthropometric measurement) in the same units to derive the following ratio indices:
Waist and hip values as well as their ratio can be interpreted using population specific cut-off points.
Table 1 highlights the "at risk" categories in Europid using waist circumference and waist-to-hip ratio according to the World Health Organisation STEPS manual.
Table 1 Risk categories for waist circumference and waist-to-hip ratios.
||At substantial risk|
≥ 90 cm (in South Asian, Japanese, Chinese)
Adapted from: WHO and Zimmet &Alberti (2006) Source [1, 15].
An overview of the characteristics of circumference methods is outlined in Table 2.
Table 2 Characteristics of circumference methods.
|Number of participants||Large|
|Researcher burden of data collection||Low|
|Researcher burden of coding and data analysis||Low|
|Risk of reactivity bias||No|
|Risk of recall bias||No|
|Risk of social desirability bias||No|
|Risk of observer bias||Yes|
|Suitability for field use||High|
|Participant literacy required||No|
Considerations relating to the use of circumference methods in specific populations are described in Table 3.
Table 3 Use of circumference methods in different populations.
|Pregnancy||Suitable, but measurements may not be reliable as unable to disentangle the maternal-fetal unit. Challenging to obtain these measurements in the last trimester as it might be difficult to identify the correct landmarks.|
|Infancy and lactation||Suitable, but no reference data available (see further considerations).|
|Toddlers and young children||Suitable, but no reference data available (see further considerations).|
|Older Adults||Suitable, but oedema may affect the ability to obtain reliable measurements especially in the leg region.|
|Ethnic groups||Suitable, but cut-off values not always available for different populations.|
|Other (obesity)||Suitable, but accurate measurements difficult to obtain as measurement locations are not always identifiable due to increase in soft tissue.|
It is recommended to estimate the technical error of measurement to monitor intra- and inter-observer variation.
Refer to section: practical considerations for objective anthropometry
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