📏 X-Height Ratio Calculator
Enter your nib's width and the nib-width ratio for your chosen script (e.g. Italic is typically 5 nib-widths) to calculate the correct x-height for consistent lettering.
Turning nib widths into millimetres
Scripts specify letter height in nib widths so the proportions survive any change of pen. This page converts that instruction into a measurement you can rule:
x-height = nib width × ratio
2 mm × 5 = 10.0 mm 0.9 mm × 4 = 3.6 mmThe defaults are an italic setting: a 2 mm nib at five nib widths gives a 10.0 mm x-height. Read it backwards when the size is fixed instead of the pen: a 7 mm x-height for a five-nib-width hand needs 7 ÷ 5 = 1.4 mm of nib. The ratio field steps in halves, so 4.5 is available.
Getting both numbers right
- Measure the nib rather than reading the label. Ink a staircase of touching square blocks and measure across it; a nib sold as 2 mm may print 1.9 or 2.1.
- Use the ratio your exemplar states. Foundational and Uncial usually run around four and Italic five. Fewer nib widths means a denser letter at the same pen size.
- Feed the answer into your ruling. A 10.0 mm x-height at two and a half times gives 25 mm baseline to baseline, with ascenders and capitals counted in the same nib widths above the line.
Frequently asked questions
What x-height should I use for italic?
Five nib widths. That is 10.0 mm with a 2 mm nib, 5.0 mm with a 1 mm nib, and 25.0 mm with a 5 mm poster nib. The millimetres change with the pen; the count of five does not.
How do I pick a nib for a fixed letter height?
Divide the height you need by the script's ratio. A 12 mm x-height in a four-nib-width hand wants a 3 mm nib; if you only have 2.5 mm, the letters come out at 10 mm instead.
Is x-height the same as the full letter height?
No. It is the body height, from baseline to the top of an x. Ascenders, descenders and capitals are measured separately, generally two to three nib widths further.