Uncertainty Principle Calculator
Calculate Heisenberg uncertainty limits for position-momentum and energy-time conjugate pairs.
About this calculator
Heisenberg's uncertainty principle sets a hard floor on how precisely position and momentum can both be known at once, and this calculator takes your chosen position uncertainty and derives every quantity that floor implies. It starts from the minimum-uncertainty case, Δx·Δp = ℏ/2, so entering a smaller position uncertainty forces the minimum momentum uncertainty higher — the two trade off directly, and no measurement can beat that product regardless of instrumentation quality. From the momentum result it derives a minimum velocity uncertainty by dividing by particle mass, and a minimum energy uncertainty from the momentum-energy relation for a free particle; the energy figure then feeds an energy-time uncertainty calculation and a de Broglie wavelength at that minimum momentum.
The ratio output simply reports how close the combination Δx·Δp sits to ℏ/2 — the calculator always sets this to exactly 1.0 because it computes the smallest possible Δp for your chosen Δx, so it's really confirming the calculator is evaluating the bound itself rather than a looser real-world measurement scenario. Because the calculator solves for the tightest case, it describes an idealized minimum-uncertainty wave packet, not the actual spread a real detector or experiment would report — real measurements typically have larger uncertainty products than this floor, never smaller. It's most useful for building intuition about scale: at atomic dimensions the position-momentum tradeoff becomes physically significant, while at everyday, human-scale distances the same relation produces uncertainties too small to ever notice.
Inputs
Results
Min Momentum Uncertainty (Δp)
0 kg·m/s
Min Velocity Uncertainty (Δv)
578,878.03 m/s
Min Energy Uncertainty (ΔE)
0 J
How to Use This Calculator
- Enter Position Uncertainty (Δx) in meters — how precisely you know the particle's location. 1e-10 m is atomic scale.
- Enter Particle Mass (kg): the default is an electron (9.109e-31 kg); a proton is 1.67e-27 kg.
- Read Min Momentum Uncertainty (Δp) — the fundamental limit imposed by Heisenberg's relation Δx·Δp ≥ ℏ/2.
- Min Velocity Uncertainty (Δv = Δp/m) shows how precisely speed can be known given the position measurement.
- The Ratio (Δx·Δp)/(ℏ/2) shows how close your measurement scenario is to the quantum limit — a value of 1.0 saturates the bound.
How the result changes with Position Uncertainty (Δx)
| Position Uncertainty (Δx) | Min Momentum Uncertainty (Δp) | Min Velocity Uncertainty (Δv) | Min Energy Uncertainty (ΔE) |
|---|---|---|---|
| 0 | 0 kg·m/s | 1,157,756.07 m/s | 0 J |
| 0 | 0 kg·m/s | 771,837.38 m/s | 0 J |
| 0 | 0 kg·m/s | 385,918.69 m/s | 0 J |
| 0 | 0 kg·m/s | 231,551.21 m/s | 0 J |
What each input means
- Position Uncertainty (Δx)
- Uncertainty in position measurement
- Particle Mass
- Mass of the particle (default: electron)
How this is calculated
Formula
Δx × Δp ≥ ℏ/2Worked example, using the default values
- Identify Input ParametersPosition Uncertainty (Δx) = 1e-10, Particle Mass = 9.109e-31 = 2 input(s) provided
- Calculate Min Momentum UncertaintyMin Momentum Uncertainty = Number(minMomentumUncertainty.toExponential(3))5.273e-25 = 5.273e-25
- Calculate Min Velocity UncertaintyMin Velocity Uncertainty578878.03 = 578878.03
- Calculate Min Energy UncertaintyMin Energy Uncertainty = Number(minEnergyUncertainty.toExponential(3))1.526e-19 = 1.526e-19
- Calculate Min Time UncertaintyMin Time Uncertainty = Number(minTimeUncertainty.toExponential(3))3.455e-16 = 3.455e-16
- Calculate Δx·Δp /Δx·Δp /1 = 1
Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does changing the particle mass leave the momentum uncertainty unchanged?
The minimum momentum uncertainty comes directly from Δp = ℏ/(2Δx), which depends only on your chosen position uncertainty, not on the mass of the particle. Mass only enters afterward, when the calculator converts that momentum uncertainty into a velocity uncertainty (Δv = Δp/m) or an energy uncertainty, both of which do depend on mass.
Why is the ratio Δx·Δp/(ℏ/2) always exactly 1.0 in the results?
Because this calculator computes the smallest momentum uncertainty consistent with your chosen position uncertainty — the minimum-uncertainty case — rather than modeling an arbitrary real measurement. Any actual experiment's uncertainty product would sit at or above 1.0, never below it, since the Heisenberg relation is a lower bound, not an equality that every measurement happens to hit.
What does a large de Broglie wavelength at minimum uncertainty actually indicate?
A longer wavelength at this minimum-momentum condition means the particle's wave-like behavior is more pronounced relative to its momentum spread, which typically happens for lighter particles or looser position constraints. It's a useful sanity check for whether quantum wave effects should matter in a given scenario versus behaving essentially classically.
Is this the uncertainty principle for a real detector or a theoretical limit?
It's the theoretical limit — a real detector's measurement uncertainty is generally larger than this bound because instrumental noise, finite resolution, and disturbance from the measurement process all add on top of the fundamental quantum floor. Treat these numbers as the best physics could ever achieve for the given position uncertainty, not what a lab instrument reports.
Related Calculators
The questions that sit next to this one — chosen by subject, including calculators filed under a different category.
Wave Function Calculator
Calculate quantum wave function properties including probability density, momentum, energy, and phase/group velocities.
Quantum PhysicsQuantum Measurement Calculator
Calculate quantum measurement probabilities, expectation values, variance, and wave function collapse.
Quantum PhysicsQuantum Foundations Calculator
Fundamental quantum mechanics calculations. Wave-particle duality, Heisenberg uncertainty, quantum harmonic oscillator, hydrogen atom, and spin.
More in Science & Physics.