There is some evidence that a scrolling design may reduce breakoffs in mobile web surveys compared to a paging design, but there is little empirical evidence to guide the choice of the optimal number of items per page. We investigate the effect of the number of items presented on a page on data quality in two types of questionnaires – with or without user-controlled skips. Three versions of a 30-item instrument were compared, with 5, 15 or all 30 questions presented on a page, in two different surveys, one with skips and one without. We found that displaying 30 items on a page reduced the breakoff rate by almost a third compared to presenting 5 items per page in the questionnaire without skips, however, the difference was not statistically significant. In both surveys with and without skips the completion times were significantly lower in the 30-item per page condition; however, item nonresponse rates were also higher. We give some practical recommendations to guide choices while designing questionnaires for mobile web surveys.