diff --git a/libraries/AP_OpticalFlow/AP_OpticalFlow_Calibrator.cpp b/libraries/AP_OpticalFlow/AP_OpticalFlow_Calibrator.cpp
new file mode 100644
index 0000000000..147fe5bba6
--- /dev/null
+++ b/libraries/AP_OpticalFlow/AP_OpticalFlow_Calibrator.cpp
@@ -0,0 +1,320 @@
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "AP_OpticalFlow_Calibrator.h"
+#include <GCS_MAVLink/GCS.h>
+#include <AP_Logger/AP_Logger.h>
+
+const uint32_t AP_OPTICALFLOW_CAL_TIMEOUT_SEC = 120;        // calibration timesout after 120 seconds
+const uint32_t AP_OPTICALFLOW_CAL_STATUSINTERVAL_SEC = 3;   // status updates printed at 3 second intervals
+const float AP_OPTICALFLOW_CAL_YAW_MAX_RADS = radians(20);  // maximum yaw rotation (must be low to ensure good scaling)
+const float AP_OPTICALFLOW_CAL_ROLLPITCH_MIN_RADS = radians(20);    // minimum acceptable roll or pitch rotation
+const float AP_OPTICALFLOW_CAL_SCALE_MIN = 0.20f;           // min acceptable scaling value.  If resulting scaling is below this then the calibration fails
+const float AP_OPTICALFLOW_CAL_SCALE_MAX = 4.0f;            // max acceptable scaling value.  If resulting scaling is above this then the calibration fails
+const float AP_OPTICALFLOW_CAL_FITNESS_THRESH = 0.5f;       // min acceptable fitness
+const float AP_OPTICALFLOW_CAL_RMS_FAILED = 1.0e30f;        // calc_mean_squared_residuals returns this value when it fails to calculate a good value
+
+extern const AP_HAL::HAL& hal;
+
+// start the calibration
+void AP_OpticalFlow_Calibrator::start()
+{
+    // exit immediately if already running
+    if (_cal_state == CalState::RUNNING) {
+        return;
+    }
+
+    _cal_state = CalState::RUNNING;
+    _start_time_ms = AP_HAL::millis();
+
+    // clear samples buffers
+    _cal_data[0].num_samples = 0;
+    _cal_data[1].num_samples = 0;
+
+    GCS_SEND_TEXT(MAV_SEVERITY_INFO, "FlowCal: Started");
+}
+
+void AP_OpticalFlow_Calibrator::stop()
+{
+    // exit immediately if already stopped
+    if (_cal_state == CalState::NOT_STARTED) {
+        return;
+    }
+
+    _cal_state = CalState::NOT_STARTED;
+
+    GCS_SEND_TEXT(MAV_SEVERITY_INFO, "FlowCal: Stopped");
+}
+
+// update the state machine and calculate scaling
+bool AP_OpticalFlow_Calibrator::update()
+{
+    // prefix for reporting
+    const char* prefix_str = "FlowCal:";
+
+    // while running add samples
+    if (_cal_state == CalState::RUNNING) {
+        uint32_t now_ms = AP_HAL::millis();
+        uint32_t timestamp_ms;
+        Vector2f flow_rate, body_rate, los_pred;
+        if (AP::ahrs().getOptFlowSample(timestamp_ms, flow_rate, body_rate, los_pred)) {
+            add_sample(timestamp_ms, flow_rate, body_rate, los_pred);
+
+            // while collecting samples display percentage complete
+            if (now_ms - _last_report_ms > AP_OPTICALFLOW_CAL_STATUSINTERVAL_SEC * 1000UL) {
+                _last_report_ms = now_ms;
+                GCS_SEND_TEXT(MAV_SEVERITY_INFO, "%s x:%d%% y:%d%%",
+                                prefix_str,
+                                (int)((_cal_data[0].num_samples * 100.0 / AP_OPTICALFLOW_CAL_MAX_SAMPLES)),
+                                (int)((_cal_data[1].num_samples * 100.0 / AP_OPTICALFLOW_CAL_MAX_SAMPLES)));
+            }
+
+            // advance state once sample buffers are full
+            if (sample_buffers_full()) {
+                _cal_state = CalState::READY_TO_CALIBRATE;
+                GCS_SEND_TEXT(MAV_SEVERITY_INFO, "%s samples collected", prefix_str);
+            }
+        }
+
+        // check for timeout
+        if (now_ms - _start_time_ms > AP_OPTICALFLOW_CAL_TIMEOUT_SEC * 1000UL) {
+            GCS_SEND_TEXT(MAV_SEVERITY_INFO, "%s timeout", prefix_str);
+            _cal_state = CalState::FAILED;
+        }
+    }
+
+    // start calibration
+    if (_cal_state == CalState::READY_TO_CALIBRATE) {
+        // run calibration and mark failure or success
+        if (run_calibration()) {
+            _cal_state = CalState::SUCCESS;
+            return true;
+        } else {
+            _cal_state = CalState::FAILED;
+        }
+    }
+
+    // return indicating calibration is not complete
+    return false;
+}
+
+// get final scaling values
+// scaling values used during sample collection should be multiplied by these scalars
+Vector2f AP_OpticalFlow_Calibrator::get_scalars()
+{
+    // return best scaling values
+    return Vector2f{_cal_data[0].best_scalar, _cal_data[1].best_scalar};
+}
+
+// add new sample to the calibrator
+void AP_OpticalFlow_Calibrator::add_sample(uint32_t timestamp_ms, const Vector2f& flow_rate, const Vector2f& body_rate, const Vector2f& los_pred)
+{
+    // return immediately if not running
+    if (_cal_state != CalState::RUNNING) {
+        return;
+    }
+
+    // check for duplicates
+    if (timestamp_ms == _last_sample_timestamp_ms) {
+        return;
+    }
+    _last_sample_timestamp_ms = timestamp_ms;
+
+    // check yaw rotation is low
+    const Vector3f gyro = AP::ahrs().get_gyro();
+    if (fabsf(gyro.z) > AP_OPTICALFLOW_CAL_YAW_MAX_RADS) {
+        return;
+    }
+
+    // check enough roll or pitch movement and record sample
+    const bool rates_x_sufficient = (fabsf(body_rate.x) >= AP_OPTICALFLOW_CAL_ROLLPITCH_MIN_RADS) && (fabsf(flow_rate.x) >= AP_OPTICALFLOW_CAL_ROLLPITCH_MIN_RADS);
+    if (rates_x_sufficient && (_cal_data[0].num_samples < ARRAY_SIZE(_cal_data[0].samples))) {
+        log_sample(0, _cal_data[0].num_samples, flow_rate.x, body_rate.x, los_pred.x);
+        _cal_data[0].samples[_cal_data[0].num_samples].flow_rate = flow_rate.x;
+        _cal_data[0].samples[_cal_data[0].num_samples].body_rate = body_rate.x;
+        _cal_data[0].samples[_cal_data[0].num_samples].los_pred = los_pred.x;
+        _cal_data[0].num_samples++;
+    }
+    const bool rates_y_sufficient = (fabsf(body_rate.y) >= AP_OPTICALFLOW_CAL_ROLLPITCH_MIN_RADS) && (fabsf(flow_rate.y) >= AP_OPTICALFLOW_CAL_ROLLPITCH_MIN_RADS);
+    if (rates_y_sufficient && (_cal_data[1].num_samples < ARRAY_SIZE(_cal_data[1].samples))) {
+        log_sample(1, _cal_data[1].num_samples, flow_rate.y, body_rate.y, los_pred.y);
+        _cal_data[1].samples[_cal_data[1].num_samples].flow_rate = flow_rate.y;
+        _cal_data[1].samples[_cal_data[1].num_samples].body_rate = body_rate.y;
+        _cal_data[1].samples[_cal_data[1].num_samples].los_pred = los_pred.y;
+        _cal_data[1].num_samples++;
+    }
+}
+
+// returns true once the sample buffer is full
+bool AP_OpticalFlow_Calibrator::sample_buffers_full() const
+{
+    return ((_cal_data[0].num_samples >= ARRAY_SIZE(_cal_data[0].samples)) && (_cal_data[1].num_samples >= ARRAY_SIZE(_cal_data[1].samples)));
+}
+
+// run calibration algorithm for both axis
+// returns true on success and updates _cal_data[0,1].best_scale and best_scale_fitness
+bool AP_OpticalFlow_Calibrator::run_calibration()
+{
+    // run calibration for x and y axis
+    const bool calx_res = calc_scalars(0, _cal_data[0].best_scalar, _cal_data[0].best_scalar_fitness);
+    const bool caly_res = calc_scalars(1, _cal_data[1].best_scalar, _cal_data[1].best_scalar_fitness);
+
+    return calx_res && caly_res;
+}
+
+// Run Gauss Newton fitting algorithm for all samples of the given axis
+// returns a scalar and fitness (lower numbers mean a better result) in the arguments provided
+bool AP_OpticalFlow_Calibrator::calc_scalars(uint8_t axis, float& scalar, float& fitness)
+{
+    // prefix for reporting
+    const char* prefix_str = "FlowCal:";
+    const char* axis_str = axis == 0 ? "x" : "y";
+
+    // check we have samples
+    // this should never fail because this method should only be called once the sample buffer is full
+    const uint8_t num_samples = _cal_data[axis].num_samples;
+    if (num_samples == 0) {
+        GCS_SEND_TEXT(MAV_SEVERITY_INFO, "%s failed because no samples", prefix_str);
+        return false;
+    }
+
+    // calculate total absolute residual from all samples
+    float total_abs_residual = 0;
+    for (uint8_t i = 0; i < num_samples; i++) {
+        const sample_t& samplei = _cal_data[axis].samples[i];
+        total_abs_residual += fabsf(calc_sample_residual(samplei, 1.0));
+    }
+
+    // if there are no residuals then scaling is perfect
+    if (is_zero(total_abs_residual)) {
+        scalar = 1.0;
+        fitness = 0;
+        GCS_SEND_TEXT(MAV_SEVERITY_INFO, "%s perfect scalar%s of 1.0", prefix_str, axis_str);
+        return true;
+    }
+
+    // for each sample calculate the residual and scalar that best reduces the residual
+    float best_scalar_total = 0;
+    for (uint8_t i = 0; i < num_samples; i++) {
+        float sample_best_scalar;
+        const sample_t& samplei = _cal_data[axis].samples[i];
+        if (!calc_sample_best_scalar(samplei, sample_best_scalar)) {
+            // failed to find the best scalar for a single sample
+            // this should never happen because of checks when capturing samples
+            GCS_SEND_TEXT(MAV_SEVERITY_INFO, "%s failed because of zero flow rate", prefix_str);
+            INTERNAL_ERROR(AP_InternalError::error_t::flow_of_control);
+            return false;
+        }
+        const float sample_residual = calc_sample_residual(samplei, 1.0);
+        best_scalar_total += sample_best_scalar * fabsf(sample_residual) / total_abs_residual;
+    }
+
+    // check for out of range results
+    if (best_scalar_total < AP_OPTICALFLOW_CAL_SCALE_MIN) {
+        GCS_SEND_TEXT(MAV_SEVERITY_INFO, "%s scalar%s:%4.3f too low (<%3.1f)", prefix_str, axis_str, (double)best_scalar_total, (double)AP_OPTICALFLOW_CAL_SCALE_MIN);
+        return false;
+    }
+    if (best_scalar_total > AP_OPTICALFLOW_CAL_SCALE_MAX) {
+        GCS_SEND_TEXT(MAV_SEVERITY_INFO, "%s scalar%s:%4.3f too high (>%3.1f)", prefix_str, axis_str, (double)best_scalar_total, (double)AP_OPTICALFLOW_CAL_SCALE_MAX);
+        return false;
+    }
+
+    // check for poor fitness
+    float fitness_new = calc_mean_squared_residuals(axis, best_scalar_total);
+    if (fitness_new > AP_OPTICALFLOW_CAL_FITNESS_THRESH) {
+        GCS_SEND_TEXT(MAV_SEVERITY_INFO, "%s scalar%s:%4.3f fit:%4.3f too high (>%3.1f)", prefix_str, axis_str, (double)scalar, (double)fitness_new, (double)AP_OPTICALFLOW_CAL_FITNESS_THRESH);
+        return false;
+    }
+
+    // success if fitness has improved
+    float fitness_orig = calc_mean_squared_residuals(axis, 1.0);
+    if (fitness_new <= fitness_orig) {
+        scalar = best_scalar_total;
+        fitness = fitness_new;
+        GCS_SEND_TEXT(MAV_SEVERITY_INFO, "%s scalar%s:%4.3f fit:%4.2f", prefix_str, axis_str, (double)scalar, (double)fitness);
+        return true;
+    }
+
+    // failed to find a better scalar than 1.0
+    scalar = 1.0;
+    fitness = fitness_orig;
+    GCS_SEND_TEXT(MAV_SEVERITY_INFO, "%s no better scalar%s:%4.3f (fit:%4.3f > orig:%4.3f)", prefix_str, axis_str, (double)best_scalar_total, (double)fitness_new, (double)fitness_orig);
+    return false;
+}
+
+// calculate a single sample's residual
+float AP_OpticalFlow_Calibrator::calc_sample_residual(const sample_t& sample, float scalar) const
+{
+    return (sample.body_rate + ((sample.flow_rate * scalar) - sample.los_pred));
+}
+
+// calculate the scalar that minimises the residual for a single sample
+// returns true on success and populates the best_scalar argument
+bool AP_OpticalFlow_Calibrator::calc_sample_best_scalar(const sample_t& sample, float& best_scalar) const
+{
+    // if sample's flow_rate is zero scalar has no effect
+    // this should never happen because samples should have been checked before being added
+    if (is_zero(sample.flow_rate)) {
+        return false;
+    }
+    best_scalar = (sample.los_pred - sample.body_rate) / sample.flow_rate;
+    return true;
+}
+
+// calculate mean squared residual for all samples of a single axis (0 or 1) given a scalar parameter
+float AP_OpticalFlow_Calibrator::calc_mean_squared_residuals(uint8_t axis, float scalar) const
+{
+    // sanity check axis
+    if (axis >= 2) {
+        return AP_OPTICALFLOW_CAL_RMS_FAILED;
+    }
+
+    // calculate and sum residuals of each sample
+    float sum = 0.0f;
+    uint16_t num_samples = 0;
+    for (uint8_t i = 0; i < _cal_data[axis].num_samples; i++) {
+        sum += sq(calc_sample_residual(_cal_data[axis].samples[i], scalar));
+        num_samples++;
+    }
+
+    // return a huge residual if no samples
+    if (num_samples == 0) {
+        return AP_OPTICALFLOW_CAL_RMS_FAILED;
+    }
+
+    sum /= num_samples;
+    return sum;
+}
+
+// log all samples
+void AP_OpticalFlow_Calibrator::log_sample(uint8_t axis, uint8_t sample_num, float flow_rate, float body_rate, float los_pred)
+{
+    // @LoggerMessage: OFCA
+    // @Description: Optical Flow Calibration sample
+    // @Field: TimeUS: Time since system startup
+    // @Field: Axis: Axis (X=0 Y=1)
+    // @Field: Num: Sample number
+    // @Field: FRate: Flow rate
+    // @Field: BRate: Body rate
+    // @Field: LPred: Los pred
+
+    AP::logger().Write("OFCA", "TimeUS,Axis,Num,FRate,BRate,LPred", "QBBfff",
+        AP_HAL::micros64(),
+        (unsigned)axis,
+        (unsigned)sample_num,
+        (double)flow_rate,
+        (double)body_rate,
+        (double)los_pred);
+}
diff --git a/libraries/AP_OpticalFlow/AP_OpticalFlow_Calibrator.h b/libraries/AP_OpticalFlow/AP_OpticalFlow_Calibrator.h
new file mode 100644
index 0000000000..5a169f2ab6
--- /dev/null
+++ b/libraries/AP_OpticalFlow/AP_OpticalFlow_Calibrator.h
@@ -0,0 +1,79 @@
+#pragma once
+
+#include <AP_HAL/AP_HAL.h>
+#include <AP_Math/AP_Math.h>
+
+#define AP_OPTICALFLOW_CAL_MAX_SAMPLES 50  // number of samples required before calibration begins
+
+class AP_OpticalFlow_Calibrator {
+public:
+    AP_OpticalFlow_Calibrator() {};
+
+    // start or stop the calibration
+    void start();
+    void stop();
+
+    // update the state machine and calculate scaling
+    // returns true if new scaling values have been found
+    bool update();
+
+    // get final scaling values
+    // scaling values used during sample collection should be multiplied by these scalars
+    Vector2f get_scalars();
+
+private:
+
+    // single sample for a single axis
+    struct sample_t {
+        float flow_rate;
+        float body_rate;
+        float los_pred;
+    };
+
+    // attempt to add a new sample to the buffer
+    void add_sample(uint32_t timestamp_ms, const Vector2f& flow_rate, const Vector2f& body_rate, const Vector2f& los_pred);
+
+    // returns true once the sample buffer is full
+    bool sample_buffers_full() const;
+
+    // run calibration algorithm for both axis
+    // returns true on success and updates _cal_data[0,1].best_scale and best_scale_fitness
+    bool run_calibration();
+
+    // Run fitting algorithm for all samples of the given axis
+    // returns a scalar and fitness (lower numbers mean a better result) in the arguments provided
+    bool calc_scalars(uint8_t axis, float& scalar, float& fitness);
+
+    // calculate a single sample's residual given a scalar parameter
+    float calc_sample_residual(const sample_t& sample, float scalar) const;
+
+    // calculate the scalar that minimises the residual for a single sample
+    // returns true on success and populates the best_scalar argument
+    bool calc_sample_best_scalar(const sample_t& sample, float& best_scalar) const;
+
+    // calculate mean squared residual for all samples of a single axis (0 or 1) given a scalar parameter
+    float calc_mean_squared_residuals(uint8_t axis, float scalar) const;
+
+    // log a sample
+    void log_sample(uint8_t axis, uint8_t sample_num, float flow_rate, float body_rate, float los_pred);
+
+    // calibration states
+    enum class CalState {
+        NOT_STARTED = 0,
+        RUNNING,            // collecting samples
+        READY_TO_CALIBRATE, // ready to calibrate (may wait until vehicle is disarmed)
+        SUCCESS,
+        FAILED
+    } _cal_state;
+
+    // local variables
+    uint32_t _start_time_ms;                                // time the calibration was started
+    struct {
+        sample_t samples[AP_OPTICALFLOW_CAL_MAX_SAMPLES];   // buffer of sensor samples
+        uint8_t num_samples;                                // number of samples in samples buffer
+        float best_scalar;                                  // best scaling value found so far
+        float best_scalar_fitness;                          // fitness (rms of error) of best scaling value
+    } _cal_data[2];                                         // x and y axis
+    uint32_t _last_sample_timestamp_ms;                     // system time of last sample's timestamp, used to ignore duplicates
+    uint32_t _last_report_ms;                               // system time of last status report
+};