The total number of people in the group you are studying. Leave blank if the population is very large (e.g., > 100,000).
90%
95% (Standard)
99%
How confident you want to be that the actual data falls within the margin of error.
The acceptable percentage of error in your results (standard is 5%).
The percentage of people you expect to actually complete the survey.
Completed Surveys Needed:0
Total Invitations to Send:0
Projected Drop-off:0
function calculateSampleSize() {
// Get Inputs
var popSizeInput = document.getElementById("popSize").value;
var zScore = parseFloat(document.getElementById("confLevel").value);
var marginError = parseFloat(document.getElementById("marginError").value);
var responseRate = parseFloat(document.getElementById("estResponseRate").value);
// Validation
if (isNaN(marginError) || marginError <= 0) {
alert("Please enter a valid Margin of Error.");
return;
}
if (isNaN(responseRate) || responseRate 0) {
// n = n0 / (1 + ((n0 – 1) / N))
sampleSize = sampleSize / (1 + ((sampleSize – 1) / popSize));
}
}
// Round up sample size to nearest whole person
var finalSampleSize = Math.ceil(sampleSize);
// Calculate invites needed based on response rate
var invitesNeeded = Math.ceil(finalSampleSize / (responseRate / 100));
// Calculate drop off (People invited who won't respond)
var dropOff = invitesNeeded – finalSampleSize;
// Display Results
document.getElementById("sampleSizeResult").innerText = finalSampleSize.toLocaleString();
document.getElementById("invitesResult").innerText = invitesNeeded.toLocaleString();
document.getElementById("dropOffResult").innerText = dropOff.toLocaleString();
document.getElementById("results").style.display = "block";
}
Understanding Survey Sample Size and Response Rates
Conducting a survey is a powerful way to gather data, but the validity of your results depends heavily on the quality of your sampling. Two critical metrics determine the success of your research: the Sample Size (how many completed surveys you need) and the Response Rate (how many invitations you must send to get those completions).
What is Sample Size?
Sample size refers to the number of completed responses you need to receive to ensure that your data accurately represents the target population. It is calculated based on three main factors:
Population Size: The total number of people in the group you are studying. For very large populations (like the population of a country), the exact number matters less.
Confidence Level: This indicates how sure you can be that your results are accurate. A 95% confidence level is the industry standard, meaning that if you repeated the survey, 95% of the time the results would match.
Margin of Error: Also known as the confidence interval, this is the range of deviation you are willing to accept. A 5% margin of error means if 60% of respondents answer "Yes," the true figure is likely between 55% and 65%.
The Impact of Response Rate
Calculating the sample size is only step one. The biggest logistical hurdle in market research is the Response Rate. This is the percentage of people who, upon receiving an invitation, actually complete the survey.
If your calculator determines you need 385 completed surveys, you cannot simply send 385 emails. If you have an average response rate of 10%, you must send out roughly 3,850 invitations to achieve your goal.
How to Use This Calculator
This tool combines statistical probability with logistical planning to give you actionable numbers for your campaign:
Enter Population: If you are surveying a specific company or list, enter the exact number. If surveying the general public, leave it blank.
Select Confidence: Stick to 95% for general business or academic research. Use 99% for high-stakes scientific studies.
Set Margin of Error: 5% is standard. Lowering this number (e.g., to 1%) will drastically increase the required sample size.
Estimate Response Rate: Be realistic. Internal employee surveys may see 30-80%, while external cold emails often yield 1-5%.
Why Your Invitation Count Matters
Underestimating the number of invitations needed is a common failure point in data collection projects. By using the "Total Invitations to Send" metric provided above, you can budget effectively for email marketing costs, panel purchases, or ad spend required to reach your statistical goals.