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Generate random numbers with a specific margin of error. Ideal for testing, simulation, and data analysis.
Random Range: 95.00 ~ 105.00
Error: ±5%
Click "Generate" to get a random value
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
Enter a target value x and a nonnegative percentage p. The tool calculates a symmetric interval around the target. Its “error percent” input means a user-chosen relative amount for this interval; it is not a statistical margin of error inferred from a survey, sample size, or confidence level, and it is not a measurement-system uncertainty estimate.
Range half-width = |target| × percentage ÷ 100
Lower bound = target − half-width; upper bound = target + half-width
For a target of 100 and 5%, the half-width is 5 and the interval is 95 to 105. For −50 at 10%, the half-width is 5 and the interval is −55 to −45. A zero target produces a zero-width interval because its absolute value is zero.
After you generate, the page draws one pseudorandom sample between the calculated bounds and rounds that result to the chosen number of decimal places. The default is two decimal places; the precision setting is clamped from zero through eight. Changing precision affects the displayed interval and rounded sample, but not the underlying interval arithmetic.
This is a simple uniform-style interval draw, not a model of measurement uncertainty or a probability distribution fitted to data. NIST’s error terminology helps distinguish relative and absolute error; the specific interval formula here is determined by the inputs described above.
Math.random(); checked 2026-09-28.Guide
Follow the workflow and verify inputs and outputs with practical examples.
Use the value you want at the center of the interval. Positive, negative, and zero values are supported.
Enter zero or a positive percentage. The control advances by 0.1, but does not set a fixed upper limit. A larger percentage makes a wider interval for any nonzero target.
Choose zero through eight places for the displayed interval and generated result.
Select Generate to see the range and one value rounded to the chosen precision. Generate again to draw another sample from the same range.
Use cases
See how the tool fits into real work and everyday tasks.
When testing how a form handles values near a target, set a percentage to define the interval and generate a sample to try manually.
Keep the target fixed and change the percentage to show how the allowable interval widens or narrows. The page returns one sample at a time rather than a list or summary statistics.
Q&A
Find concise answers to common questions and confusing cases.
Each click draws a new pseudorandom sample within the current bounds and rounds it to the selected precision. The range stays the same unless you change its inputs.
The percentage is applied to the target’s absolute value, and that half-width is added to and subtracted from the target. For example, −50 at 10% gives bounds of −55 and −45.
No. It changes how many decimal places are shown and how the generated sample is rounded, not the underlying formula.
Notes
Review scope, result limitations, and important precautions before use.
This tool creates a random example inside a user-defined interval. It does not estimate survey margin of error, calibrate an instrument, measure a real quantity, or choose an uncertainty model from observations. For formal measurement uncertainty, use the applicable measurement method and instrument specifications.
The generated values use ordinary pseudorandom behavior and are not suitable for passwords, cryptographic keys, security tokens, or any draw that requires a cryptographically secure random source. Treat them as examples or simple test inputs, not as evidence that a real measurement falls within the chosen range.
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