Why does a larger size reduce the simulated blur?

Because the blur is applied as a fixed pixel radius while the letterforms grow around it. Effective blur is the simulation value scaled by sixteen divided by the current size, so the same visual impairment costs proportionally less detail at 24px than at 14px. That relationship is the whole reason size is the first lever for older readers.

Why recommend 18px when many designs use 16px?

Because the recommendation is aimed at readers whose accommodation has already narrowed, not at a general audience. The table puts the minimum at 18px with 19 to 20px preferred, and it treats 16px as a floor for younger readers rather than a target for this one. A design can hold 16px and still pass if the weight and contrast carry the rest.

Is the contrast filter a real measure of retinal illuminance?

No, it is a simulation. It combines the ratio you enter with a base factor so the preview loses contrast as the ratio drops and stops changing once the ratio is high enough. It is shaped to look like the effect rather than to reproduce a measured response curve, and it is there to make a comparison visible.

Should I raise weight or contrast first?

Size first, then weight, then contrast, in that order, because that is their order of effect on the simulated result. Weight matters most when the face is light and the strokes are thin, whereas contrast only helps while the pair is below the enhanced threshold; beyond about 12 to 1 there is little left to gain.

Can it simulate a specific eye condition?

Not a specific one. The simulator models the two changes that account for most of the difference for older readers, reduced accommodation and reduced retinal illuminance, and leaves out field loss, floaters and the scattering that cataracts cause. For the scattering case, the glare and halation preset in the low vision font tester is the closer approximation.

Font for Elderly Simulator

Type settings

Font family

Sizepx

Weight

Contrast:1

Simulated acuity losspx

Sample text

Effective blur at this size1.20px

AAA body contrast (7:1)passes

Size checkbelow 18px — raise it

Simulated reading experience

Presbyopia reduces the eye's ability to focus at close range, so small text appears blurred even with good contrast.

As size grows, the same acuity loss blurs proportionally less — which is why raising size is the single most effective change, ahead of weight or even contrast.

Recommended settings

Setting	Current	Target
Minimum body size	16px	18px (19–20px preferred)
Minimum weight	400	400 at 18px, 500 below that
Text contrast	10:1	7:1 or better; 12:1+ for long reading
Line height	1.5 (typical)	1.6–1.8
Paragraph spacing	1em	1.2–1.5em so paragraphs separate at a glance

css output

.elder-friendly {
  font-family: 'Source Serif 4', serif;
  font-size: max(1.125rem, 1.0000rem); /* ≥18px */
  font-weight: 400;
  line-height: 1.7;
  letter-spacing: 0.01em;
  color: #111;      /* ≥7:1 on a light surface */
  max-width: 68ch;
}

You Might Also Need

Low Vision Font Tester

Test fonts for low vision

WCAG Font Size Checker

Check sizes against WCAG

Line Height Optimizer

Optimize leading for readability

Mobile Font Size Checker

Verify mobile text sizes

The font for elderly simulator renders a sample under the two effects that dominate reading for older eyes, then recommends the size, weight and contrast that recover most of the loss. Presbyopia reduces the eye's ability to focus at close range while a narrowing pupil lowers retinal illuminance, and both are modelled in the preview.

What is Font for Elderly Simulator?

The font for elderly simulator applies a blur and a contrast reduction to a text sample, modelling presbyopia and the loss of contrast sensitivity that comes with it, then reports what the type setting would have to be for the same sample to read comfortably, with the CSS to produce it.

The blur control models simulated acuity loss from 0 to 3px in tenths, defaulting to 1.2px.
Contrast runs from 1 to 1 to 21 to 1 in half steps, defaulting to 10 to 1.
Size spans 12px to 40px, weight from 300 to 700 in hundred-unit steps, and the sample text is editable.
Faces come from the built-in catalogue with Source Serif 4 as the starting choice.
The recommendation table covers five settings: minimum body size of 18px with 19 to 20px preferred, minimum weight of 400 at 18px and 500 below it, contrast of 7 to 1 or better with 12 to 1 and above for long reading, line height of 1.6 to 1.8, and paragraph spacing of 1.2 to 1.5em.

The point of the preview is that the same acuity loss blurs proportionally less as the type grows. The effective blur is the blur value multiplied by sixteen and divided by the size, so at 16px a 1.2px simulation stays at 1.2px while at 24px it falls to 0.8px, which is why raising size is the most effective single change, ahead of weight and even contrast. Retinal illuminance is modelled as a contrast filter that combines the entered ratio with a base factor, so the preview darkens as the ratio drops and stops improving once the ratio is high enough that the filter reaches full strength. The panel also grades the setting directly: contrast at or above 7 to 1 satisfies the enhanced body text requirement, and a size of 18px or more is what the check looks for, with the exported CSS writing the size as a maximum of 1.125rem and the current value so it can never fall below the recommended floor.

Two effects are modelled, accommodation and pupil size, which between them account for much of the change but not all of it; field loss, floaters and cataract haze are not represented.
The blur is uniform across the sample, where real acuity loss varies with distance from the fixation point and with the letterform itself.
The contrast filter approximates retinal illuminance rather than simulating a measured response curve.
The checks are coarse by design: contrast passes at 7 to 1 and size passes at 18px, with no credit for being close.
This is a design aid, not a clinical tool, and nothing here measures a real reader's vision.

Use it when an audience skews older and a design has been approved on a young reviewer's screen, since the failure mode is almost always a body size chosen for density rather than for the reader. Raise size first, then weight, then contrast, in that order, because that is the order of their effect on the simulated result. Comparing conditions rather than a single one belongs to the low vision font tester, the size thresholds for a text style are itemised by the WCAG font size checker, and the leading recommendation in the table is the same problem the line height optimizer solves at a fixed measure.

How to use Font for Elderly Simulator

Enter the type setting you are reviewing: face, size, weight and the contrast ratio the pair achieves, plus the sample text you want judged.
Set the simulated acuity loss, starting around 1.2px, and watch the effective blur readout as you change the size.
Compare the simulated reading experience against the recommended settings table, noting which rows your current values miss.
Copy the exported CSS, which floors the size at 1.125rem and the weight at 400, and adjust the contrast pair if the 7 to 1 row is failing.

When to use Font for Elderly Simulator vs related tools

Reach for it when a product serves an older audience and a body size has been chosen for density, when a design review keeps producing the comment that the text feels small, or when a client needs to see why 14px body text fails a large part of its readership. It is the quickest of the simulators to explain, because a single blur slider makes the argument without numbers. For a comparison of several conditions rather than one, the low vision font tester applies acuity, glare and contrast sensitivity side by side, the WCAG font size checker states the size and spacing thresholds formally, and the line height optimizer settles the leading the recommendation table asks for.

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