diff --git a/src/libcalamares/CMakeLists.txt b/src/libcalamares/CMakeLists.txt
index c4b9fa40c..bc3ce0511 100644
--- a/src/libcalamares/CMakeLists.txt
+++ b/src/libcalamares/CMakeLists.txt
@@ -22,6 +22,9 @@ set( libSources
     ProcessJob.cpp
     Settings.cpp
 )
+set( partSources
+    partition/PartitionSize.cpp
+)
 set( utilsSources
     utils/CalamaresUtilsSystem.cpp
     utils/CommandList.cpp
@@ -72,7 +75,7 @@ if( WITH_PYTHON )
     )
 endif()
 
-add_library( calamares SHARED ${libSources} ${kdsagSources} ${utilsSources} )
+add_library( calamares SHARED ${libSources} ${kdsagSources} ${partSources} ${utilsSources} )
 set_target_properties( calamares
     PROPERTIES
         VERSION ${CALAMARES_VERSION_SHORT}
diff --git a/src/libcalamares/partition/PartitionSize.cpp b/src/libcalamares/partition/PartitionSize.cpp
new file mode 100644
index 000000000..edff0fe1e
--- /dev/null
+++ b/src/libcalamares/partition/PartitionSize.cpp
@@ -0,0 +1,238 @@
+/* === This file is part of Calamares - <https://github.com/calamares> ===
+ *
+ *   Copyright 2019, Collabora Ltd <arnaud.ferraris@collabora.com>
+ *
+ *   Calamares 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.
+ *
+ *   Calamares 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 Calamares. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "partition/PartitionSize.h"
+#include "utils/Logger.h"
+#include "utils/Units.h"
+
+namespace Calamares
+{
+
+static const NamedEnumTable<SizeUnit>&
+unitSuffixes()
+{
+    static const NamedEnumTable<SizeUnit> names{
+        { QStringLiteral( "%" ), SizeUnit::Percent },
+        { QStringLiteral( "K" ), SizeUnit::KiB },
+        { QStringLiteral( "KiB" ), SizeUnit::KiB },
+        { QStringLiteral( "M" ), SizeUnit::MiB },
+        { QStringLiteral( "MiB" ), SizeUnit::MiB },
+        { QStringLiteral( "G" ), SizeUnit::GiB },
+        { QStringLiteral( "GiB" ), SizeUnit::GiB }
+    };
+
+    return names;
+}
+
+PartitionSize::PartitionSize( const QString& s )
+    : NamedSuffix( unitSuffixes(), s )
+{
+    if ( ( unit() == unit_t::Percent ) && ( value() > 100 || value() < 0 ) )
+    {
+        cDebug() << "Percent value" << value() << "is not valid.";
+        m_value = 0;
+    }
+
+    if ( m_unit == unit_t::None )
+    {
+        m_value = s.toInt();
+        if ( m_value > 0 )
+            m_unit = unit_t::Byte;
+    }
+
+    if ( m_value <= 0 )
+    {
+        m_value = 0;
+        m_unit = unit_t::None;
+    }
+}
+
+qint64
+PartitionSize::toSectors( qint64 totalSectors, qint64 sectorSize ) const
+{
+    if ( !isValid() )
+        return -1;
+    if ( totalSectors < 1 || sectorSize < 1 )
+        return -1;
+
+    switch ( m_unit )
+    {
+    case unit_t::None:
+        return -1;
+    case unit_t::Percent:
+        if ( value() == 100 )
+            return totalSectors;  // Common-case, avoid futzing around
+        else
+            return totalSectors * value() / 100;
+    case unit_t::Byte:
+    case unit_t::KiB:
+    case unit_t::MiB:
+    case unit_t::GiB:
+        return CalamaresUtils::bytesToSectors ( toBytes(), sectorSize );
+    }
+
+    return -1;
+}
+
+qint64
+PartitionSize::toBytes( qint64 totalSectors, qint64 sectorSize ) const
+{
+    if ( !isValid() )
+        return -1;
+
+    switch ( m_unit )
+    {
+    case unit_t::None:
+        return -1;
+    case unit_t::Percent:
+        if ( totalSectors < 1 || sectorSize < 1 )
+            return -1;
+        if ( value() == 100 )
+            return totalSectors * sectorSize;  // Common-case, avoid futzing around
+        else
+            return totalSectors * value() / 100;
+    case unit_t::Byte:
+    case unit_t::KiB:
+    case unit_t::MiB:
+    case unit_t::GiB:
+        return toBytes();
+    }
+
+    // notreached
+    return -1;
+}
+
+qint64
+PartitionSize::toBytes( qint64 totalBytes ) const
+{
+    if ( !isValid() )
+        return -1;
+
+    switch ( m_unit )
+    {
+    case unit_t::None:
+        return -1;
+    case unit_t::Percent:
+        if ( totalBytes < 1 )
+            return -1;
+        if ( value() == 100 )
+            return totalBytes;  // Common-case, avoid futzing around
+        else
+            return totalBytes * value() / 100;
+    case unit_t::Byte:
+    case unit_t::KiB:
+    case unit_t::MiB:
+    case unit_t::GiB:
+        return toBytes();
+    }
+
+    // notreached
+    return -1;
+}
+
+qint64
+PartitionSize::toBytes() const
+{
+    if ( !isValid() )
+        return -1;
+
+    switch ( m_unit )
+    {
+    case unit_t::Byte:
+        return value();
+    case unit_t::KiB:
+        return CalamaresUtils::KiBtoBytes( static_cast<unsigned long long>( value() ) );
+    case unit_t::MiB:
+        return CalamaresUtils::MiBtoBytes( static_cast<unsigned long long>( value() ) );
+    case unit_t::GiB:
+        return CalamaresUtils::GiBtoBytes( static_cast<unsigned long long>( value() ) );
+    default:
+        break;
+    }
+
+    // Reached only when unit is Percent or None
+    return -1;
+}
+
+bool
+PartitionSize::operator< ( const PartitionSize& other ) const
+{
+    if ( ( m_unit == unit_t::None    || other.m_unit == unit_t::None    ) ||
+         ( m_unit == unit_t::Percent && other.m_unit != unit_t::Percent ) ||
+         ( m_unit != unit_t::Percent && other.m_unit == unit_t::Percent ) )
+        return false;
+
+    switch ( m_unit )
+    {
+    case unit_t::Percent:
+        return ( m_value < other.m_value );
+    case unit_t::Byte:
+    case unit_t::KiB:
+    case unit_t::MiB:
+    case unit_t::GiB:
+        return ( toBytes() < other.toBytes () );
+    }
+
+    return false;
+}
+
+bool
+PartitionSize::operator> ( const PartitionSize& other ) const
+{
+    if ( ( m_unit == unit_t::None    || other.m_unit == unit_t::None    ) ||
+         ( m_unit == unit_t::Percent && other.m_unit != unit_t::Percent ) ||
+         ( m_unit != unit_t::Percent && other.m_unit == unit_t::Percent ) )
+        return false;
+
+    switch ( m_unit )
+    {
+    case unit_t::Percent:
+        return ( m_value > other.m_value );
+    case unit_t::Byte:
+    case unit_t::KiB:
+    case unit_t::MiB:
+    case unit_t::GiB:
+        return ( toBytes() > other.toBytes () );
+    }
+
+    return false;
+}
+
+bool
+PartitionSize::operator== ( const PartitionSize& other ) const
+{
+    if ( ( m_unit == unit_t::None    || other.m_unit == unit_t::None    ) ||
+         ( m_unit == unit_t::Percent && other.m_unit != unit_t::Percent ) ||
+         ( m_unit != unit_t::Percent && other.m_unit == unit_t::Percent ) )
+        return false;
+
+    switch ( m_unit )
+    {
+    case unit_t::Percent:
+        return ( m_value == other.m_value );
+    case unit_t::Byte:
+    case unit_t::KiB:
+    case unit_t::MiB:
+    case unit_t::GiB:
+        return ( toBytes() == other.toBytes () );
+    }
+
+    return false;
+}
+
+} // namespace Calamares
diff --git a/src/libcalamares/partition/PartitionSize.h b/src/libcalamares/partition/PartitionSize.h
new file mode 100644
index 000000000..13ffa5c70
--- /dev/null
+++ b/src/libcalamares/partition/PartitionSize.h
@@ -0,0 +1,103 @@
+/* === This file is part of Calamares - <https://github.com/calamares> ===
+ *
+ *   Copyright 2019, Collabora Ltd <arnaud.ferraris@collabora.com>
+ *
+ *   Calamares 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.
+ *
+ *   Calamares 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 Calamares. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef PARTITION_PARTITIONSIZE_H
+#define PARTITION_PARTITIONSIZE_H
+
+#include "utils/Units.h"
+#include "utils/NamedSuffix.h"
+
+// Qt
+#include <QString>
+
+namespace Calamares
+{
+
+enum class SizeUnit
+{
+    None,
+    Percent,
+    Byte,
+    KiB,
+    MiB,
+    GiB
+};
+
+/** @brief Partition size expressions
+ *
+ * Sizes can be specified in bytes, KiB, MiB, GiB or percent (of
+ * the available drive space are on). This class handles parsing
+ * of such strings from the config file.
+ */
+class PartitionSize : public NamedSuffix<SizeUnit, SizeUnit::None>
+{
+public:
+    PartitionSize() : NamedSuffix() { }
+    PartitionSize( int v, unit_t u ) : NamedSuffix( v, u ) { }
+    PartitionSize( const QString& );
+
+    bool isValid() const
+    {
+        return ( unit() != SizeUnit::None ) && ( value() > 0 );
+    }
+
+    bool operator< ( const PartitionSize& other ) const;
+    bool operator> ( const PartitionSize& other ) const;
+    bool operator== ( const PartitionSize& other ) const;
+
+    /** @brief Convert the size to the number of sectors @p totalSectors .
+     *
+     * Each sector has size @p sectorSize, for converting sizes in Bytes,
+     * KiB, MiB or GiB to sector counts.
+     *
+     * @return  the number of sectors needed, or -1 for invalid sizes.
+     */
+    qint64 toSectors( qint64 totalSectors, qint64 sectorSize ) const;
+
+    /** @brief Convert the size to bytes.
+     *
+     * The device's sectors count @p totalSectors and sector size
+     * @p sectoreSize are used to calculated the total size, which
+     * is then used to calculate the size when using Percent.
+     *
+     * @return  the size in bytes, or -1 for invalid sizes.
+     */
+    qint64 toBytes( qint64 totalSectors, qint64 sectorSize ) const;
+
+    /** @brief Convert the size to bytes.
+     *
+     * Total size @p totalBytes is needed for sizes in Percent. This
+     * parameter is unused in any other case.
+     *
+     * @return  the size in bytes, or -1 for invalid sizes.
+     */
+    qint64 toBytes( qint64 totalBytes ) const;
+
+    /** @brief Convert the size to bytes.
+     *
+     * This method is only valid for sizes in Bytes, KiB, MiB or GiB.
+     * It will return -1 in any other case.
+     *
+     * @return  the size in bytes, or -1 if it cannot be calculated.
+     */
+    qint64 toBytes() const;
+};
+
+} // namespace Calamares
+
+#endif // PARTITION_PARTITIONSIZE_H