diff --git a/app/autonomy/LocalizationMeasurements.js b/app/autonomy/LocalizationMeasurements.js
index 7a46c6d..0a30fa0 100644
--- a/app/autonomy/LocalizationMeasurements.js
+++ b/app/autonomy/LocalizationMeasurements.js
@@ -33,6 +33,17 @@ export function gaussianSample(rng) {
     return Math.sqrt(-2 * Math.log(left)) * Math.cos(2 * Math.PI * rng.next());
 }
 
+/**
+ * Per-sample standard deviation, on every axis, for white noise given as a
+ * datasheet noise density (units/√Hz): sigma = density / √dt. Without a
+ * density, returns `perSample` unchanged.
+ */
+export function noiseStdDevFromDensity(density, perSample, dtSeconds) {
+    if (density == null) return perSample;
+    const sigma = Math.max(0, Number(density)) / Math.sqrt(Math.max(Number.EPSILON, dtSeconds));
+    return { x: sigma, y: sigma, z: sigma };
+}
+
 export function sampleAxisNoise(rng, stdDev, bias = { x: 0, y: 0, z: 0 }, drift = { x: 0, y: 0, z: 0 }) {
     const perturb = (axis) => (Number(bias[axis] || 0) + Number(drift[axis] || 0))
         + gaussianSample(rng) * Number(stdDev[axis] || 0);
@@ -252,15 +263,25 @@ export function buildImuMeasurement(snapshot, sensorConfig, rng, state = {}) {
         ),
     };
 
+    const angularStdDev = noiseStdDevFromDensity(
+        noise.angularVelocityNoiseDensity ?? sensorConfig.calibration.angularVelocityNoiseDensity,
+        noise.angularVelocityStdDev || sensorConfig.calibration.angularVelocityStdDev || { x: 0, y: 0, z: 0 },
+        dt,
+    );
+    const accelerationStdDev = noiseStdDevFromDensity(
+        noise.linearAccelerationNoiseDensity ?? sensorConfig.calibration.linearAccelerationNoiseDensity,
+        noise.linearAccelerationStdDev || sensorConfig.calibration.linearAccelerationStdDev || { x: 0, y: 0, z: 0 },
+        dt,
+    );
     const angularNoise = sampleAxisNoise(
         rng,
-        noise.angularVelocityStdDev || sensorConfig.calibration.angularVelocityStdDev || { x: 0, y: 0, z: 0 },
+        angularStdDev,
         turnOnBias.angular || turnOnBias,
         nextDrift.angular,
     );
     const accelerationNoise = sampleAxisNoise(
         rng,
-        noise.linearAccelerationStdDev || sensorConfig.calibration.linearAccelerationStdDev || { x: 0, y: 0, z: 0 },
+        accelerationStdDev,
         turnOnBias.acceleration || { x: 0, y: 0, z: 0 },
         nextDrift.acceleration,
     );
@@ -281,8 +302,8 @@ export function buildImuMeasurement(snapshot, sensorConfig, rng, state = {}) {
             angularVelocity: measuredAngular,
             linearAcceleration: measuredAcceleration,
             orientationCovariance: unavailableOrientationCovariance(),
-            angularVelocityCovariance: diagonalCovariance(noise.angularVelocityStdDev || sensorConfig.calibration.angularVelocityStdDev || { x: 0, y: 0, z: 0 }),
-            linearAccelerationCovariance: diagonalCovariance(noise.linearAccelerationStdDev || sensorConfig.calibration.linearAccelerationStdDev || { x: 0, y: 0, z: 0 }),
+            angularVelocityCovariance: diagonalCovariance(angularStdDev),
+            linearAccelerationCovariance: diagonalCovariance(accelerationStdDev),
         },
         nextState: {
             turnOnBias,
diff --git a/app/simulation/sensors/SensorTypeRegistry.js b/app/simulation/sensors/SensorTypeRegistry.js
index 10162f0..64ff1b0 100644
--- a/app/simulation/sensors/SensorTypeRegistry.js
+++ b/app/simulation/sensors/SensorTypeRegistry.js
@@ -159,8 +159,10 @@ function axisCalibration(source = {}, fallback = 0) {
 const imuRunFields = [
     { label: "Gravity (m/s²)", path: ["calibration", "gravity"], control: "number", min: 0, step: 0.001 },
     { label: "IMU topic ID", path: ["outputs", "imuTopicId"], control: "text", advanced: true },
-    { label: "Angular velocity σ (rad/s)", path: ["calibration", "angularVelocityStdDev", "x"], control: "number", min: 0, step: 0.0001, advanced: true },
-    { label: "Linear acceleration σ (m/s²)", path: ["calibration", "linearAccelerationStdDev", "z"], control: "number", min: 0, step: 0.001, advanced: true },
+    { label: "Gyro noise density (rad/s/√Hz)", path: ["calibration", "angularVelocityNoiseDensity"], control: "number", min: 0, step: 0.00001, advanced: true },
+    { label: "Accelerometer noise density (m/s²/√Hz)", path: ["calibration", "linearAccelerationNoiseDensity"], control: "number", min: 0, step: 0.0001, advanced: true },
+    { label: "Angular velocity σ per sample (rad/s), without density", path: ["calibration", "angularVelocityStdDev", "x"], control: "number", min: 0, step: 0.0001, advanced: true },
+    { label: "Linear acceleration σ per sample (m/s²), without density", path: ["calibration", "linearAccelerationStdDev", "z"], control: "number", min: 0, step: 0.001, advanced: true },
     { label: "Angular saturation (rad/s)", path: ["calibration", "angularVelocitySaturation"], control: "number", min: 0, advanced: true },
     { label: "Acceleration saturation (m/s²)", path: ["calibration", "linearAccelerationSaturation"], control: "number", min: 0, advanced: true },
 ];
diff --git a/docs/run-manifests.md b/docs/run-manifests.md
index a8c36ae..b6d2cf8 100644
--- a/docs/run-manifests.md
+++ b/docs/run-manifests.md
@@ -356,10 +356,28 @@ appearance/analytic readback.
 
 | Sensor | Rate | Key calibration | Units |
 | --- | --- | --- | --- |
+| IMU | 100 Hz | `gravity`, `angularVelocityNoiseDensity`, `linearAccelerationNoiseDensity` (or per-sample `angularVelocityStdDev`, `linearAccelerationStdDev`), drift τ, saturation | rad/s/√Hz, m/s²/√Hz (rad/s, m/s² per sample) |
+| GNSS | 10 Hz | `datum` (lat/lng/alt), `positionNoiseEnu`, `faults.dropoutProbability`, `faults.outageProbability`, multipath τ | deg, m |
 | IMU | 100 Hz | `gravity`, per-axis `angularVelocityStdDev`, `linearAccelerationStdDev`, drift τ, saturation | rad/s, m/s² |
 | GNSS | 10 Hz | `datum` (lat/lng/alt), `positionNoiseEnu`, `faults.dropoutProbability`, `faults.outageProbability`, `faults.outageDurationSec` (0 or absent: outage lasts to the end of the run), multipath τ | deg, m |
 | Wheel odometry | 50 Hz | `wheelRadius`, `ticksPerRevolution`, `trackWidth`, `slipFactor`, pose/twist noise | m, ticks/rev |
 
+IMU white noise is set from datasheet noise densities. Each sample gets
+σ = density / √Δt, where Δt is the time since the previous capture. Raising
+the rate then raises per-sample noise, and noise averaged over a fixed time
+stays the same, as on a real sensor. Each density is one number for all
+three axes. Without a density, the IMU uses the per-sample
+`angularVelocityStdDev` or `linearAccelerationStdDev`, which does not scale
+with rate. Default runs set no density. The per-sample defaults
+(0.002 rad/s, 0.02 m/s²) equal 0.0002 rad/s/√Hz and 0.002 m/s²/√Hz at 100 Hz.
+
+Datasheet conversions:
+
+- gyro °/s/√Hz × π/180 = rad/s/√Hz
+- gyro angle random walk °/√h × π/180 / 60 = rad/s/√Hz
+- accelerometer µg/√Hz × 9.80665e-6 = m/s²/√Hz
+- accelerometer velocity random walk m/s/√h ÷ 60 = m/s²/√Hz
+
 GNSS treats map/odom position as ENU offset from the manifest datum. Wheel odometry integrates an independent measured `odom → base_link` estimate; oracle truth on `/oracle/vehicle/odometry` remains isolated for scoring.
 
 ## Headless profiles, spaces, and sensor backends