Forms & Signup
Testing a Taller Input Field Height on a Form
Taller input fields provide larger touch targets and may make mobile entry easier. They also lengthen the form and reduce how many fields fit on screen. Compare completion while keeping font size and spacing unchanged.
A/B test scenario. This page is a test plan, not the result of a real experiment.
- Forms & signup
- Form completion rate
Control vs Variant
The same element, larger or smaller.
- Changed
- Size
- Page
- Forms & signup
- Difference
- changed
Hypothesis
If input fields are taller, they are easier to hit on a touchscreen and visitors may tap the wrong field less often. On mobile in particular, the form completion rate could improve, while fewer fields fitting on screen could lower the form start rate.
Test plan
When to run this test
Session recordings of visitors tapping the wrong field and going back, a higher validation error rate on mobile than on desktop, or longer form completion time on mobile are signs that fields are hard to hit on touch devices. Taller fields should then cut mobile input errors and let more visitors submit the form. If the struggle shows up only on desktop, or the errors come from visitors not knowing what format a field expects, review the instructions and error messages before touching field height.
How to measure success
Form completion rate
Compare successful submissions to see whether taller fields affect completion.
Also track
- Form start rateCompare visitors who begin the first field after seeing the form.
- Form completion timeMeasure time from form start to successful submission.
- Validation error rateTrack input and validation errors that may relate to field height.
How to set it up
- HeightIncrease field height by a predefined amount.
- Keep constantKeep font size, spacing between fields, field width, order and validation unchanged.
- Touch inputMeasure mobile input errors the same way in both arms.
- DensityRead start and abandonment rates alongside the number of fields visible at once.
- DeviceReview desktop and touch devices separately.
What to watch when reading the result
- 1Weigh the form completion rate against the form start rate; when fewer fields fit on screen, fewer visitors may begin. If the loss in starts cancels out the gain in completion, the taller fields are not worth shipping.
- 2Interpret touch devices and desktop separately; a desktop result tells you nothing about tapping behavior on mobile. What you measured is specific to this height and this form, so test again for a different height or a shorter form. If you want to try smaller fields, keep touch targets at or above the accessibility minimum; going below it is not a test option.
- 3With a small or unclear difference, first check whether the touch-device segment, where the effect is expected, had enough traffic. Planning this up front with the sample size calculator keeps you from ending up with an underpowered result once you split by device.
Frequently Asked Questions
How can field height affect form completion?
Use valid form completion as the primary outcome. Form starts and visible-field counts are diagnostic. Taller fields may improve tapping while making the form appear longer.
Does desktop data show the touchscreen effect?
No. Inspect touch-device behavior and input errors separately. Desktop interaction cannot establish whether a larger target improves mobile entry.
Can a smaller-field variant also be tested?
Only if the control remains accessible and usable. This scenario compares standard and increased height. Do not introduce targets below applicable accessibility requirements.
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