diff --git a/src/functionObjects/field/Make/files b/src/functionObjects/field/Make/files
index b666221d3a..1afdfb2ea7 100644
--- a/src/functionObjects/field/Make/files
+++ b/src/functionObjects/field/Make/files
@@ -3,6 +3,7 @@ fieldAverage/fieldAverageItem/fieldAverageItem.C
 fieldAverage/fieldAverageItem/fieldAverageItemIO.C
 
 fieldCoordinateSystemTransform/fieldCoordinateSystemTransform.C
+fieldExtents/fieldExtents.C
 fieldMinMax/fieldMinMax.C
 
 fieldValues/fieldValue/fieldValue.C
diff --git a/src/functionObjects/field/fieldExtents/fieldExtents.C b/src/functionObjects/field/fieldExtents/fieldExtents.C
new file mode 100644
index 0000000000..8e65a802eb
--- /dev/null
+++ b/src/functionObjects/field/fieldExtents/fieldExtents.C
@@ -0,0 +1,201 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2018 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM 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.
+
+    OpenFOAM 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 OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "fieldExtents.H"
+#include "addToRunTimeSelectionTable.H"
+
+// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
+
+namespace Foam
+{
+namespace functionObjects
+{
+    defineTypeNameAndDebug(fieldExtents, 0);
+    addToRunTimeSelectionTable(functionObject, fieldExtents, dictionary);
+}
+}
+
+
+// * * * * * * * * * * * * Protected Member Functions  * * * * * * * * * * * //
+
+void Foam::functionObjects::fieldExtents::writeFileHeader(Ostream& os)
+{
+    if (!fieldSet_.updateSelection())
+    {
+        return;
+    }
+
+    if (writtenHeader_)
+    {
+        writeBreak(os);
+    }
+    else
+    {
+        writeHeader(os, "Field extents");
+        writeHeaderValue(os, "Reference position", C0_);
+        writeHeaderValue(os, "Threshold", threshold_);
+    }
+
+    writeCommented(os, "Time");
+
+    forAllConstIters(fieldSet_.selection(), iter)
+    {
+        const word& fieldName = iter();
+        if (internalField_)
+        {
+            writeTabbed(os, fieldName + "_internal");
+        }
+        for (const label patchi : patchIDs_)
+        {
+            const word& patchName = mesh_.boundaryMesh()[patchi].name();
+            writeTabbed(os, fieldName + "_" + patchName);
+        }
+    }
+
+    os  << endl;
+
+    writtenHeader_ = true;
+}
+
+
+template<>
+Foam::tmp<Foam::volScalarField> Foam::functionObjects::fieldExtents::calcMask
+(
+    const GeometricField<scalar, fvPatchField, volMesh>& field
+) const
+{
+    return
+        pos
+        (
+            field
+          - dimensionedScalar("t", field.dimensions(), threshold_)
+        );
+}
+
+
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+Foam::functionObjects::fieldExtents::fieldExtents
+(
+    const word& name,
+    const Time& runTime,
+    const dictionary& dict
+)
+:
+    fvMeshFunctionObject(name, runTime, dict),
+    writeFile(mesh_, name, typeName, dict),
+    internalField_(true),
+    threshold_(0),
+    C0_(Zero),
+    fieldSet_(mesh_),
+    patchIDs_()
+{
+    read(dict);
+
+    // Note: delay creating the output file header to handle field names
+    // specified using regular expressions
+}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+bool Foam::functionObjects::fieldExtents::read(const dictionary& dict)
+{
+    if (fvMeshFunctionObject::read(dict) && writeFile::read(dict))
+    {
+        threshold_ = dict.get<scalar>("threshold");
+
+        dict.readIfPresent<bool>("internalField", internalField_);
+
+        dict.readIfPresent<vector>("referencePosition", C0_);
+
+        patchIDs_.clear();
+        const polyBoundaryMesh& pbm = mesh_.boundaryMesh();
+
+        wordReList patchNames;
+        if (dict.readIfPresent("patches", patchNames))
+        {
+            for (const wordRe& name : patchNames)
+            {
+                patchIDs_.insert(pbm.findIndices(name));
+            }
+        }
+        else
+        {
+            // Add all non-processor and non-empty patches
+            forAll(pbm, patchi)
+            {
+                const polyPatch& pp = pbm[patchi];
+                if (!isA<processorPolyPatch>(pp) && !isA<emptyPolyPatch>(pp))
+                {
+                    patchIDs_.insert(patchi);
+                }
+            }
+        }
+
+        if (!internalField_ && patchIDs_.empty())
+        {
+            IOWarningInFunction(dict)
+                << "No internal field or patches selected - no field extent "
+                << "information will be generated" << endl;
+        }
+
+        fieldSet_.read(dict);
+
+        return true;
+    }
+
+    return false;
+}
+
+
+bool Foam::functionObjects::fieldExtents::execute()
+{
+    return true;
+}
+
+
+bool Foam::functionObjects::fieldExtents::write()
+{
+    writeFileHeader(file());
+
+    Log << type() << " " << name() <<  " write:" << nl;
+
+    for (const word& fieldName : fieldSet_.selection())
+    {
+        calcFieldExtents<scalar>(fieldName, true);
+        calcFieldExtents<vector>(fieldName);
+        calcFieldExtents<sphericalTensor>(fieldName);
+        calcFieldExtents<symmTensor>(fieldName);
+        calcFieldExtents<tensor>(fieldName);
+    }
+
+    Log << endl;
+
+    return true;
+}
+
+
+// ************************************************************************* //
diff --git a/src/functionObjects/field/fieldExtents/fieldExtents.H b/src/functionObjects/field/fieldExtents/fieldExtents.H
new file mode 100644
index 0000000000..9d4d8ac939
--- /dev/null
+++ b/src/functionObjects/field/fieldExtents/fieldExtents.H
@@ -0,0 +1,207 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2018 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM 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.
+
+    OpenFOAM 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 OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Class
+    Foam::functionObjects::fieldExtents
+
+Group
+    grpFieldFunctionObjects
+
+Description
+    Calculates the spatial minimum and maximum extents of a field
+
+    The extents are derived from the bound box limits after identifying the
+    locations where field values exceed the user-supplied threshold value.
+
+Usage
+    Example of function object specification:
+    \verbatim
+    fieldExtents1
+    {
+        type        fieldExtents;
+        libs        ("libfieldFunctionObjects.so");
+        ...
+        writeToFile yes;
+        log         yes;
+        fields      (alpha);
+        threshold   0.5;
+        patches     ();
+    }
+    \endverbatim
+
+    Where the entries comprise:
+    \table
+        Property      | Description              | Required   | Default value
+        type          | type name: fieldExtents  | yes        |
+        writeToFile   | write extents data to file | no       | yes
+        log           | write extents data to standard output | no | yes
+        internalField | Process the internal field | no       | yes
+        threshold     | Field value to identify extents boundary | yes |
+        referencePosition | Reference position   | no         | (0 0 0)
+        fields        | list of fields to process | yes       |
+        patches       | list of patches to process | no       | \<all patches\>
+    \endtable
+
+    Output data is written to the file \<timeDir\>/fieldExtents.dat
+
+Note
+    For non-scalar fields, the magnitude of the field is employed and compared
+    to the threshold value.
+
+See also
+    Foam::functionObjects::fvMeshFunctionObject
+    Foam::functionObjects::writeFile
+
+SourceFiles
+    fieldExtents.C
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef functionObjects_fieldExtents_H
+#define functionObjects_fieldExtents_H
+
+#include "fvMeshFunctionObject.H"
+#include "writeFile.H"
+#include "volFieldSelection.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+namespace functionObjects
+{
+
+/*---------------------------------------------------------------------------*\
+                        Class fieldExtents Declaration
+\*---------------------------------------------------------------------------*/
+
+class fieldExtents
+:
+    public fvMeshFunctionObject,
+    public writeFile
+{
+protected:
+
+    // Protected data
+
+        //- Flag to write the internal field extents
+        bool internalField_;
+
+        //- Threshold value
+        scalar threshold_;
+
+        //- Reference position; default = (0 0 0)
+        point C0_;
+
+        //- Fields to assess
+        volFieldSelection fieldSet_;
+
+        //- Patches to assess
+        labelHashSet patchIDs_;
+
+
+    // Protected Member Functions
+
+        //- Output file header information
+        virtual void writeFileHeader(Ostream& os);
+
+        //- Return the field mask
+        template<class Type>
+        tmp<volScalarField> calcMask
+        (
+            const GeometricField<Type, fvPatchField, volMesh>& field
+        ) const;
+
+        //- Main calculation
+        template<class Type>
+        void calcFieldExtents
+        (
+            const word& fieldName,
+            const bool calcMag = false
+        );
+
+        //- No copy construct
+        fieldExtents(const fieldExtents&) = delete;
+
+        //- No copy assignment
+        void operator=(const fieldExtents&) = delete;
+
+
+public:
+
+    //- Runtime type information
+    TypeName("fieldExtents");
+
+
+    // Constructors
+
+        //- Construct from Time and dictionary
+        fieldExtents
+        (
+            const word& name,
+            const Time& runTime,
+            const dictionary& dict
+        );
+
+
+    //- Destructor
+    virtual ~fieldExtents() = default;
+
+
+    // Member Functions
+
+        //- Read the field extents data
+        virtual bool read(const dictionary&);
+
+        //- Execute, currently does nothing
+        virtual bool execute();
+
+        //- Write the fieldExtents
+        virtual bool write();
+};
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+template<>
+tmp<volScalarField> fieldExtents::calcMask
+(
+    const GeometricField<scalar, fvPatchField, volMesh>& field
+) const;
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace functionObjects
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#ifdef NoRepository
+    #include "fieldExtentsTemplates.C"
+#endif
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //
diff --git a/src/functionObjects/field/fieldExtents/fieldExtentsTemplates.C b/src/functionObjects/field/fieldExtents/fieldExtentsTemplates.C
new file mode 100644
index 0000000000..9ea87aef7d
--- /dev/null
+++ b/src/functionObjects/field/fieldExtents/fieldExtentsTemplates.C
@@ -0,0 +1,120 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2018 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM 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.
+
+    OpenFOAM 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 OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "fieldExtents.H"
+#include "volFields.H"
+#include "boundBox.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+template<class Type>
+Foam::tmp<Foam::volScalarField> Foam::functionObjects::fieldExtents::calcMask
+(
+    const GeometricField<Type, fvPatchField, volMesh>& field
+) const
+{
+    return
+        pos
+        (
+            mag(field)
+          - dimensionedScalar("t", field.dimensions(), threshold_)
+        );
+}
+
+
+template<class Type>
+void Foam::functionObjects::fieldExtents::calcFieldExtents
+(
+    const word& fieldName,
+    const bool calcMag
+)
+{
+    typedef GeometricField<Type, fvPatchField, volMesh> VolFieldType;
+
+    const VolFieldType* fieldPtr =
+        obr_.lookupObjectPtr<VolFieldType>(fieldName);
+
+    if (!fieldPtr)
+    {
+        return;
+    }
+
+    auto extents = [this](const scalarField& mask, const vectorField& C)
+    {
+        boundBox extents(boundBox::invertedBox);
+        forAll(mask, i)
+        {
+            if (mask[i] > 0.5)
+            {
+                extents.add(C[i] - C0_);
+            }
+        };
+
+        extents.reduce();
+
+        if (extents.empty())
+        {
+            extents.add(point::zero);
+        }
+
+        return extents;
+    };
+
+    Log << "field: " << fieldName << nl;
+
+    writeTime(file());
+
+    tmp<volScalarField> tmask = calcMask<Type>(*fieldPtr);
+    const volScalarField& mask = tmask();
+
+    // Internal field
+    if (internalField_)
+    {
+        boundBox bb(extents(mask, mesh_.C()));
+        Log << "    internal field: " << bb << nl;
+        file() << bb;
+
+        this->setResult(fieldName + "_internal_min" , bb.min());
+        this->setResult(fieldName + "_internal_max", bb.max());
+    }
+
+    // Patches
+    for (const label patchi : patchIDs_)
+    {
+        const fvPatchScalarField& maskp = mask.boundaryField()[patchi];
+        boundBox bb(extents(maskp, maskp.patch().Cf()));
+        const word& patchName = maskp.patch().name();
+        Log << "    patch " << patchName << ": " << bb << nl;
+        file() << bb;
+        this->setResult(fieldName + "_" + patchName + "_min", bb.min());
+        this->setResult(fieldName + "_" + patchName + "_max", bb.max());
+    }
+
+    Log << endl;
+    file() << endl;
+}
+
+
+// ************************************************************************* //
diff --git a/tutorials/lagrangian/reactingParcelFoam/rivuletPanel/system/controlDict b/tutorials/lagrangian/reactingParcelFoam/rivuletPanel/system/controlDict
index b628460e8e..363963055d 100644
--- a/tutorials/lagrangian/reactingParcelFoam/rivuletPanel/system/controlDict
+++ b/tutorials/lagrangian/reactingParcelFoam/rivuletPanel/system/controlDict
@@ -51,5 +51,18 @@ maxCo           0.3;
 
 maxDeltaT       1e-03;
 
+functions
+{
+    fieldExtents
+    {
+        type            fieldExtents;
+        libs            ("libfieldFunctionObjects.so");
+        region          wallFilmRegion;
+        threshold       0.5;
+        fields          (alpha);
+        internalField   yes;
+        patches         ();
+    }
+}
 
 // ************************************************************************* //