Fonts 5% bigger site-wide: +6.91% revenue per visitor
Test run byDave DiederenSyntra Labs
Commentary byLiftArchiveOur analysis, not theirsMaking all fonts 5% bigger lifted revenue per visitor by 6.91% in Dave Diederen's test, from $1.16 to $1.25. Conversion rate rose 5.41% and average order value rose slightly. The confidence ranges all crossed zero, so this leans positive but isn't certain.
- Revenue per visitor: +6.91% ($1.16 to $1.25). The range ran from -7% to +22%, so the true effect could be flat.
- Conversion rate: +5.41% (2.68% to 2.83%), range -4% to +16%. A few more visitors placed an order.
- Average order value: +1.42% ($43.42 to $44.04), range -8% to +12%. Effectively flat.
- The tool estimated about +461 orders and +$25,587 in revenue a month.
The change
The variant scales up all text by 5%; the layout is otherwise the same.
Simplified mockup drawn by LiftArchive from the shared screenshots.
Control
The store with its original font sizes.
Variant
The same store with text scaled up by 5%. Nothing else changed in the layout, according to the variant name.
Why it likely won
Our reading of the result, not the practitioner's claim.
- Dave Diederen argues many shoppers are older and browse on small, older phones, where small body text is tiring to read.
- when copy is easier to read, shoppers take in more of the product details and reassurance on the page.
- designers often judge type on large, sharp screens, so the default size can be smaller than buyers need.
Caveats: All three ranges crossed zero, so the lift may not hold. Sample size, test length and the starting font size were not shared.
Who ran it
Dave Diederen (@DaveDiederen) shared this test on X. The numbers and screenshots are theirs.
View the original post on X
How to run this test on your store
- Hypothesis
- If we increase font sizes across the store, then more visitors will buy because product information is easier to read on mobile.
- Primary metric
- Revenue per visitor
- Guardrails
- Average order value
- Mobile bounce rate
- Layout breakage on small screens
- Who should test it
- Stores with small mobile body text, especially those selling to buyers aged 40 and up. If your body copy is already 16px or larger, expect less.
Questions
Does font size affect conversion rate?
In this test, a 5% bigger font lifted conversion by 5.41% and revenue per visitor by 6.91%. The ranges crossed zero, so treat it as a likely win, not a sure one.
What font size should mobile body text be?
Dave Diederen suggests checking that mobile body copy is at least 16px. The post does not say what size the store started at.
Did bigger fonts change order value?
Barely. Average order value rose 1.42%, which is within noise. The gain came mostly from more visitors buying.
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