Survey Length Calculator: Estimate Interview Length (LOI)
Estimate how long your questionnaire takes by question type, device and language before fieldwork. Editable timings, section breakdown and length warnings.
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How to use the survey length calculator
- Count the questions in your draft by type. For grids, count the total number of statements (rows), not the number of grids.
- Enter the share of respondents you expect on mobile and, for translated surveys, how much longer the translation runs.
- Choose the interview mode.
- Open Timing assumptions to adjust the seconds per item if you have your own data.
The estimate is a median: half of respondents will be faster and half slower. Use it to quote, to set incentives and to decide what to cut before you program.
Why survey length matters
Length of interview (LOI) drives cost, incentive levels and data quality. Panel providers usually price by LOI and incidence. Long surveys see more drop-outs, more straight-lining in grids and shorter open-ended answers near the end. Many researchers aim to keep online surveys under 15 to 20 minutes, and under 10 for mobile-first audiences.
How the estimate works
Each question type has a typical answering time. Single-choice questions take a few seconds; open-ended questions take the longest; grid rows are quick individually but add up. The calculator adds these, plus reading time for instructions at about 200 words per minute, then applies three adjustments:
- Device: smartphone respondents are usually slower on the same questionnaire.
- Language: translations often run longer than English, which adds reading time.
- Mode: interviewer-led telephone and face-to-face interviews take longer than self-completion.
The defaults are starting points, not universal constants. Your soft launch is the real test: field 20–50 interviews, check the median time, and update the assumptions.
Worked example
A brand health survey has 8 screener questions, 18 single-choice, 8 multi-choice, 45 grid statements, 6 numeric, 4 open-ends, a 6-item ranking, 10 MaxDiff tasks, 3 concepts and a 30-second video, with 400 words of instructions. 70% will answer on mobile and the German translation is 20% longer.
The estimate is about 28 minutes, far too long for a mostly mobile audience. Cutting the grids to 25 statements, dropping one open-end and halving MaxDiff to 5 tasks brings it to about 23 minutes. Removing the ranking and two more single-choice questions gets it close to 22. Press Example to load it and try the cuts yourself.
Tips to shorten a survey
- Remove questions whose answers will not change a decision.
- Pipe or skip: only ask follow-ups to the people they apply to.
- Split long grids into blocks of 6 to 8 statements, and drop statements that measure the same thing.
- Replace open-ends with a coded list plus "other, specify" where you can.
- Move demographics you can get from the panel profile out of the questionnaire.
Frequently asked questions
How long should an online survey be?
Ideally 10 to 15 minutes. Up to 20 minutes works for engaged audiences such as physicians or B2B decision-makers when incentives match. Beyond 20, quality usually suffers.
How many questions fit in 10 minutes?
Roughly 35 to 50 simple closed questions, or fewer if there are grids, open-ends or stimuli.
What is LOI in market research?
Length of interview: the median time a qualified respondent takes to complete the survey. It is one of the main inputs to fieldwork pricing.
How do I spot respondents who rush?
Flag completes much faster than the median, commonly under 30–50% of it. The speeder and data quality calculator does this from your completion times.
Need the respondents, not just the numbers?
Global Vox Populi runs quantitative and qualitative fieldwork in 170+ countries through its own proprietary panels of consumers, B2B and IT decision-makers, physicians, nurses, patients, caregivers and payers. ISO 9001, ISO 20252 and ISO/IEC 27001 certified and HIPAA compliant, following ESOMAR and Insights Association guidelines.
Check feasibilityLink to this tool
Free to use in proposals, courses and articles. If it helped, a link back is appreciated:
<a href="https://globalvoxpopuli.com/tools/survey-length-calculator/">Survey Length (LOI) Calculator</a> by Global Vox Populi