Type size, units and measuring instruments

Created by: Marcela Romero.

Artículo en proceso de traducción

It is essential to correctly understand what a letter is and how it should be measured. Basic knowledge of typography and of most of graphic design is based on the concept of type size.

Type size

It is the vertical measure of the type’s front face, taking the complete lead block, not only the printing area of a specific letter. Therefore, this value is the same for capitals, lower case letters, numbers, punctuation marks, and other components of the case, whether they have ascenders and descenders or not.

The type size, a standardized measure measurable in the lead block, includes variable heights according to typeface families, ascenders, “x” height, descenders and a small space (called shoulder) for the descenders in the line above not to touch ascenders in the line below. We say that these areas are variable because they depend on the design of the typeface family.

Partes de un tipo móvil

Partes de un tipo móvil


Gets its name from small metallic rulers that were used to widen the space between the lines in a text composed in movable types. Leading is the distance between a line of text and the following one, measured, for example, from baseline to baseline. When this measure coincides with font size, the difference between them is zero. This value is called solid leading.

If the distance between lines is smaller than the type size that composes the text, we will get a negative leading. This process, which today we can easily access thanks to digital technology, was impossible to carry out with lead types.

The size corresponding to leading is indicated after the type size, separated by a dash. When composing different typeface families in a same type size we will see that the support on the baseline coincides, but the heights of capitals, ascenders, “x” and descenders may not. Each typeface family was designed with its own criteria, starting even from different units of measurement to give proportions to the signs.

To equal type size correspond equal front face heights, but without the movable type the size has become intangible and it has been impossible to reach a consensus as to what should be measured in the printed sign.

Cuerpo e interlineado

Ejemplo: Garamond, Univers, Bodoni


In order to establish some relations we have to agree on nomenclature:
A typeface family is built between by 5 main lines:
Baseline or standard (s): it is the one on which the signs rest. It is maintained when composing letters from different typeface families or in different type sizes. Above the baseline is the lower case “x” or “x” height (without ascenders); The capitals height (m) and the ascender height (a). In many typeface families the latter two coincide, in others the ascenders are higher. Below the baseline is the descenders’ line (d). But we can also talk about the following dimensions:

También podemos hablar de las siguientes dimensiones: “H”, o tamaño de las mayúsculas; “k”, o tamaño de las ascendentes; “p”, o tamaño de las descendentes; “x”, o tamaño de la equis; y “kp” u “ojo”, que es la distancia entre las dos líneas extremas (k y p). En pocas ocasiones kp coincide con el cuerpo, lo que equivale a decir que en el tipo metálico no hay hombro superior ni inferior.

Estableceremos relaciones entre estas dimensiones y, además, entre estas y el cuerpo. Las proporciones que podemos establecer entre cuerpo/H, cuerpo/kp, cuerpo x, h/k o kp/x nos permiten encontrar puntos de referencia cuando analizamos o comparamos familias.

  • H, or capitals height
  • k, or ascenders height
  • p, or descenders height
  • x, or “x” height
  • kp or type face, which is the distance between the two extreme lines (k and p).
  • In rare occasions kp coincides with the type size, which is the same as saying that in the metallic type there is no shoulder. We will establish relations between these dimensions and between them and the type size: The proportions we can establish between type size/H, type size/kp, type size/x, h/k or kp/x allow us to find reference points when analyzing or comparing families.

    Type size/kp: This relation shows us the area occupied by the type face in the movable type or, in other words, the proportion the shoulders have to separate a line from another in a solid leading. The smaller this index, the tighter the lines look (less shoulder). This relation should be taken into account when planning the leading in a certain family.

    The number type size/kp represents the blank space between lines without leading (solid). When small, it indicates that the ascenders in the lower line are close to the descenders in the line above (therefore the type face occupies almost all the surface of the face of the type). It is probable that a letter with a high percentage of kp will need a wider leading than one with a low percentage of kp.

    kp/x: This is essential in order to know a family. When we say that a family has a high or low “x” height, we are referring to this proportion.

    Families with different kp/x relations composed in the same type size show different printed areas, so much that we could mistake them as having different type sizes or leading.

    Relaciones cuerpo/kp

    Other relations

    The quotient type size/H indicates which is the size of capitals in relation to type size. We can also establish relations between k and p, for example to know the proportion in which ascenders are longer than descenders. If we make (k-p)/k we will obtain this relation. If the result of this quotient is negative, we would have a family where descenders are longer than ascenders, which is rare.

    Otras relaciones

    Jorge de Buen Unna propone tomar Univers 55 como referencia para comparar las relaciones, por haber sido diseñada por Frutiger con la intención de ser un tipo universal. Se podrían formar tablas muy sencillas a partir de relaciones geométricas más descriptivas, que en el caso de Univers serían igual a 1 y calcularse rápidamente las diferencias con este «modelo».

    The fact that type size is not a measurable dimension today is quite inconvenient, but different attempts to normalize the size of printed signs have not had good results.

    The identity of each typeface family is given, among other things, by its structure, defined by proportions, type of curves and terminals. Therefore, to use kp or H or x as a normalized dimension for a specific type size restricts this decision and leaves an indissoluble aspect of characters out of the system: its counterform. We have already seen that for a set of signs to behave like a family, not only its form is important but also its spacing, both horizontal and vertical.

    On the other hand, these «size normalizations» are once again so incomplete at defining letter size as the size of the lead block in typographic printing and do not solve the problem.

    Cuadro de atributos de caracteres

    Units of Measurement

    American system (AA), the most widely known in the world, because in most desktop publishing programs is taken as master system; and Didot, used in many European countries. In both systems the unit of measurement is called point, and its abbreviation is pt. Thus, as they are different measuring systems, it is necessary to make it clear which system we refer to in each case.

    Twelve AA points conform a pica and 12 Didot points conform a Cicero. The AA point is slightly smaller than the Didot point (see equivalences).

    These two systems, apart from being used for measuring type sizes, are used when projecting text applications on pages and when building typographic grids, as we shall see later on.

    Measurement instruments

    In order to measure typography, two different tools may be used: the first and most precise one is the typometer or typographic ruler, consisting of a metal or celluloid ruler, with series of lines repeated several times, with a fixed value space between them, which are placed on text lines until the adequate value is found by comparison. The second one, less precise than the first one, consists of a celluloid sheet with groups of letters printed on it (generally capitals, lower case with ascenders, descenders and without them) in different type sizes, which are registered under each group. Putting this ruler on the texts to be measured, one can obtain an approximation of its type size.

    Today, the use of computers and desktop publishing programs have made many of the stages of the design process easier, being one of them the measurement of type size. The process consists of selecting the text to be measured or modified, then entering the desired value in a box in a dialogue window that each program presents.


    • SOLOMON, Martin. El arte de la tipografía, Tellus, Madrid.
    • RUDER, Emil. Manual de diseño tipográfico, G. Gili, Madrid.
    • DE BUEN UNNA, Jorge.  Manual de diseño editorial. 3.ª edición, corregida y aumentada. Trea Ediciones, España, 2009.
    • MARTINEZ DE SOUSA, José. Manual de edición y autoedición, Ediciones Pirámide. 1999.
    • GÁLVEZ PIZARRO, Francisco. Educación tipográfica, una introducción a la tipografía, Universidad Diego Portales, Chile, 2004.

    This entry is also available in: Spanish

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