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About this tool
Tune optical letter-spacing per font size, weight and case, with a live preview and copyable em, px and 1/1000 em values.
The Letter Spacing Tuner calculates the letter-spacing value a given font size, weight and case should use, expressed in em, pixels and the 1/1000 em unit design apps expect. It applies the optical tracking curve tracking = A + B·e^(C·size) — the exponential fit that makes small text open up and display text tighten — then adds documented corrections for heavy weights, all-caps settings and light-on-dark text. Designers and front-end developers get a defensible starting value plus a live preview instead of guessing at round numbers.
Open Letter Spacing Tuner on AltFTool — it loads instantly in your browser.
Paste or type the text you're working with.
Choose how it should be transformed or analyzed.
Copy the finished text into your document or post.
Tracking follows an exponential curve against font size rather than one fixed value.
Every result is shown in CSS em, rendered pixels and Photoshop's 1/1000 em tracking unit.
The base curve and each correction are listed separately so you can justify the number.
Large headings usually need negative tracking, converging on about -0.022em once the size passes roughly 40px. The optical curve reaches that floor because letterforms at display size already look far apart, so tightening restores the word shape.
Around +0.06em, or 60/1000 em, is the standard editorial allowance for all-caps text. Capitals have no ascenders or descenders to interlock, so without extra tracking the letters read as a solid block; small caps need about half that.
Use em. Letter-spacing in em scales with the font size automatically, so a single value survives responsive size changes, whereas a px value that looks right at 48px will be far too wide at 16px.
Light glyphs on a dark ground bloom optically — an effect called halation — which visually thins the gaps between letters. Opening reversed text by roughly 0.005em restores the rhythm of the same setting printed dark-on-light.