diff --git a/src/ViewportWidget.cpp b/src/ViewportWidget.cpp
index d843ffc..e3ccd96 100644
--- a/src/ViewportWidget.cpp
+++ b/src/ViewportWidget.cpp
@@ -198,20 +198,48 @@ void ViewportWidget::paintGL()
 
     if (m_isDefiningLine && m_activeTool == static_cast<int>(ApplicationController::ToolType::Line)) {
         vertices.clear();
-        QVector3D worldPos = unproject(m_currentMousePos, m_currentPlane);
-        if (m_isSnappingOrigin) {
-            worldPos.setX(0); worldPos.setY(0); worldPos.setZ(0);
-        } else if (m_isSnappingVertex) {
-            worldPos.setX(m_snapVertex.X()); worldPos.setY(m_snapVertex.Y()); worldPos.setZ(m_snapVertex.Z());
-        } else if (m_isSnappingHorizontal) {
-            if (m_currentPlane == SketchPlane::XY) worldPos.setZ(m_firstLinePoint.Z());
-            else if (m_currentPlane == SketchPlane::XZ) worldPos.setY(m_firstLinePoint.Y());
-            else if (m_currentPlane == SketchPlane::YZ) worldPos.setZ(m_firstLinePoint.Z());
-        } else if (m_isSnappingVertical) {
-            if (m_currentPlane == SketchPlane::XY) worldPos.setX(m_firstLinePoint.X());
-            else if (m_currentPlane == SketchPlane::XZ) worldPos.setX(m_firstLinePoint.X());
-            else if (m_currentPlane == SketchPlane::YZ) worldPos.setY(m_firstLinePoint.Y());
+        QVector3D worldPos;
+        QVector3D startPos(m_firstLinePoint.X(), m_firstLinePoint.Y(), m_firstLinePoint.Z());
+
+        QString dimInput = property("dimensionInput").toString();
+        bool lengthFromInput = false;
+        if (!dimInput.isEmpty()) {
+            bool ok;
+            double inputLength = dimInput.toDouble(&ok);
+            if (ok) {
+                lengthFromInput = true;
+                QVector3D currentMouseWorldPos = unproject(m_currentMousePos, m_currentPlane);
+                QVector3D dir = (currentMouseWorldPos - startPos);
+                if (dir.length() > 1e-6) {
+                    dir.normalize();
+                    worldPos = startPos + inputLength * dir;
+                } else {
+                    if (m_currentPlane == SketchPlane::XY || m_currentPlane == SketchPlane::XZ) {
+                        worldPos = startPos + QVector3D(inputLength, 0, 0);
+                    } else {
+                        worldPos = startPos + QVector3D(0, inputLength, 0);
+                    }
+                }
+            }
         }
+
+        if (!lengthFromInput) {
+            worldPos = unproject(m_currentMousePos, m_currentPlane);
+            if (m_isSnappingOrigin) {
+                worldPos.setX(0); worldPos.setY(0); worldPos.setZ(0);
+            } else if (m_isSnappingVertex) {
+                worldPos.setX(m_snapVertex.X()); worldPos.setY(m_snapVertex.Y()); worldPos.setZ(m_snapVertex.Z());
+            } else if (m_isSnappingHorizontal) {
+                if (m_currentPlane == SketchPlane::XY) worldPos.setZ(m_firstLinePoint.Z());
+                else if (m_currentPlane == SketchPlane::XZ) worldPos.setY(m_firstLinePoint.Y());
+                else if (m_currentPlane == SketchPlane::YZ) worldPos.setZ(m_firstLinePoint.Z());
+            } else if (m_isSnappingVertical) {
+                if (m_currentPlane == SketchPlane::XY) worldPos.setX(m_firstLinePoint.X());
+                else if (m_currentPlane == SketchPlane::XZ) worldPos.setX(m_firstLinePoint.X());
+                else if (m_currentPlane == SketchPlane::YZ) worldPos.setY(m_firstLinePoint.Y());
+            }
+        }
+
         vertices << m_firstLinePoint.X() << m_firstLinePoint.Y() << m_firstLinePoint.Z();
         vertices << worldPos.x() << worldPos.y() << worldPos.z();
 
@@ -220,7 +248,58 @@ void ViewportWidget::paintGL()
         m_vbo.allocate(vertices.constData(), vertices.size() * sizeof(GLfloat));
         glDrawArrays(GL_LINES, 0, 2);
 
-        if (m_isSnappingHorizontal || m_isSnappingVertical) {
+        // Draw dimension line
+        QVector3D lineVec = worldPos - startPos;
+        float lineLength = lineVec.length();
+
+        if (lineLength > 1e-6) {
+            vertices.clear();
+
+            QVector3D perpVec;
+            if (m_currentPlane == SketchPlane::XY) {
+                perpVec = QVector3D(-lineVec.z(), 0, lineVec.x()).normalized();
+            } else if (m_currentPlane == SketchPlane::XZ) {
+                perpVec = QVector3D(-lineVec.y(), lineVec.x(), 0).normalized();
+            } else if (m_currentPlane == SketchPlane::YZ) {
+                perpVec = QVector3D(0, -lineVec.z(), lineVec.y()).normalized();
+            }
+
+            float offset = 0.05f * -m_camera->zoom();
+            QVector3D dimStart = startPos + offset * perpVec;
+            QVector3D dimEnd = worldPos + offset * perpVec;
+
+            vertices << dimStart.x() << dimStart.y() << dimStart.z();
+            vertices << dimEnd.x() << dimEnd.y() << dimEnd.z();
+
+            float arrowLength = 0.02f * -m_camera->zoom();
+            float arrowWidth = 0.005f * -m_camera->zoom();
+            QVector3D lineDir = lineVec.normalized();
+
+            QVector3D arrow_base_end = dimEnd - arrowLength * lineDir;
+            QVector3D arrowP1_end = arrow_base_end + arrowWidth * perpVec;
+            QVector3D arrowP2_end = arrow_base_end - arrowWidth * perpVec;
+            vertices << dimEnd.x() << dimEnd.y() << dimEnd.z();
+            vertices << arrowP1_end.x() << arrowP1_end.y() << arrowP1_end.z();
+            vertices << dimEnd.x() << dimEnd.y() << dimEnd.z();
+            vertices << arrowP2_end.x() << arrowP2_end.y() << arrowP2_end.z();
+
+            QVector3D arrow_base_start = dimStart + arrowLength * lineDir;
+            QVector3D arrowP1_start = arrow_base_start + arrowWidth * perpVec;
+            QVector3D arrowP2_start = arrow_base_start - arrowWidth * perpVec;
+            vertices << dimStart.x() << dimStart.y() << dimStart.z();
+            vertices << arrowP1_start.x() << arrowP1_start.y() << arrowP1_start.z();
+            vertices << dimStart.x() << dimStart.y() << dimStart.z();
+            vertices << arrowP2_start.x() << arrowP2_start.y() << arrowP2_start.z();
+
+            m_shaderProgram->setUniformValue(m_colorLoc, QVector4D(0.7f, 0.7f, 0.7f, 1.0f));
+            glLineWidth(1.0f);
+            m_vbo.bind();
+            m_vbo.allocate(vertices.constData(), vertices.size() * sizeof(GLfloat));
+            glDrawArrays(GL_LINES, 0, vertices.size() / 3);
+            glLineWidth(2.0f);
+        }
+
+        if (!lengthFromInput && (m_isSnappingHorizontal || m_isSnappingVertical)) {
             vertices.clear();
             QVector3D startPos(m_firstLinePoint.X(), m_firstLinePoint.Y(), m_firstLinePoint.Z());
             QVector3D midPoint = (startPos + worldPos) / 2.0;
@@ -273,6 +352,91 @@ void ViewportWidget::paintGL()
     }
     m_featureBrowser->paint(painter, width(), height());
 
+    if (m_isDefiningLine && m_activeTool == static_cast<int>(ApplicationController::ToolType::Line)) {
+        QVector3D worldPos;
+        QVector3D startPos(m_firstLinePoint.X(), m_firstLinePoint.Y(), m_firstLinePoint.Z());
+        QString dimText;
+
+        QString dimInput = property("dimensionInput").toString();
+        bool lengthFromInput = false;
+        double lineLength = 0;
+
+        if (!dimInput.isEmpty()) {
+            bool ok;
+            double inputLength = dimInput.toDouble(&ok);
+            if (ok) {
+                lengthFromInput = true;
+                lineLength = inputLength;
+                QVector3D currentMouseWorldPos = unproject(m_currentMousePos, m_currentPlane);
+                QVector3D dir = (currentMouseWorldPos - startPos);
+                if (dir.length() > 1e-6) {
+                    dir.normalize();
+                    worldPos = startPos + inputLength * dir;
+                } else {
+                    if (m_currentPlane == SketchPlane::XY || m_currentPlane == SketchPlane::XZ) {
+                        worldPos = startPos + QVector3D(inputLength, 0, 0);
+                    } else {
+                        worldPos = startPos + QVector3D(0, inputLength, 0);
+                    }
+                }
+            }
+        }
+
+        if (!lengthFromInput) {
+            worldPos = unproject(m_currentMousePos, m_currentPlane);
+            if (m_isSnappingOrigin) {
+                worldPos.setX(0); worldPos.setY(0); worldPos.setZ(0);
+            } else if (m_isSnappingVertex) {
+                worldPos.setX(m_snapVertex.X()); worldPos.setY(m_snapVertex.Y()); worldPos.setZ(m_snapVertex.Z());
+            } else if (m_isSnappingHorizontal) {
+                if (m_currentPlane == SketchPlane::XY) worldPos.setZ(m_firstLinePoint.Z());
+                else if (m_currentPlane == SketchPlane::XZ) worldPos.setY(m_firstLinePoint.Y());
+                else if (m_currentPlane == SketchPlane::YZ) worldPos.setZ(m_firstLinePoint.Z());
+            } else if (m_isSnappingVertical) {
+                if (m_currentPlane == SketchPlane::XY) worldPos.setX(m_firstLinePoint.X());
+                else if (m_currentPlane == SketchPlane::XZ) worldPos.setX(m_firstLinePoint.X());
+                else if (m_currentPlane == SketchPlane::YZ) worldPos.setY(m_firstLinePoint.Y());
+            }
+            lineLength = (worldPos - startPos).length();
+        }
+
+        QVector3D lineVec = worldPos - startPos;
+        if (lineVec.length() > 1e-6) {
+            QVector3D perpVec;
+            if (m_currentPlane == SketchPlane::XY) {
+                perpVec = QVector3D(-lineVec.z(), 0, lineVec.x()).normalized();
+            } else if (m_currentPlane == SketchPlane::XZ) {
+                perpVec = QVector3D(-lineVec.y(), lineVec.x(), 0).normalized();
+            } else if (m_currentPlane == SketchPlane::YZ) {
+                perpVec = QVector3D(0, -lineVec.z(), lineVec.y()).normalized();
+            }
+
+            float offset = 0.05f * -m_camera->zoom();
+            QVector3D dimStart = startPos + offset * perpVec;
+            QVector3D dimEnd = worldPos + offset * perpVec;
+            QVector3D textPos3D = (dimStart + dimEnd) / 2.0f + 0.015f * -m_camera->zoom() * perpVec;
+
+            QVector3D screenPos = project(textPos3D, model, projection, rect());
+
+            if (screenPos.z() < 1.0f) {
+                dimText = lengthFromInput ? dimInput : QString::number(lineLength, 'f', 2);
+
+                painter.setRenderHint(QPainter::Antialiasing);
+                QFontMetrics fm(painter.font());
+                QRect textRect = fm.boundingRect(dimText + "_");
+                textRect.moveCenter(screenPos.toPoint());
+
+                if (lengthFromInput) {
+                    painter.fillRect(textRect.adjusted(-4, -2, 4, 2), QColor(64, 128, 255));
+                } else {
+                    painter.fillRect(textRect.adjusted(-4, -2, 4, 2), QColor(50, 50, 50));
+                }
+                painter.setPen(Qt::white);
+                painter.drawText(textRect, Qt::AlignCenter, dimText);
+            }
+        }
+    }
+
     painter.end();
 }
 
@@ -318,9 +482,11 @@ void ViewportWidget::mousePressEvent(QMouseEvent *event)
         if (!m_isDefiningLine) {
             m_firstLinePoint = p;
             m_isDefiningLine = true;
+            setProperty("dimensionInput", QVariant(""));
         } else {
             emit lineAdded(m_firstLinePoint, p);
             m_firstLinePoint = p;
+            setProperty("dimensionInput", QVariant(""));
             }
             update();
         }
@@ -462,9 +628,53 @@ void ViewportWidget::wheelEvent(QWheelEvent *event)
 
 void ViewportWidget::keyPressEvent(QKeyEvent *event)
 {
+    if (m_isDefiningLine && m_activeTool == static_cast<int>(ApplicationController::ToolType::Line)) {
+        QString currentInput = property("dimensionInput").toString();
+        if (event->key() >= Qt::Key_0 && event->key() <= Qt::Key_9) {
+            currentInput += event->text();
+            setProperty("dimensionInput", currentInput);
+            update();
+            return;
+        } else if (event->key() == Qt::Key_Period) {
+            if (!currentInput.contains('.')) {
+                currentInput += '.';
+                setProperty("dimensionInput", currentInput);
+                update();
+                return;
+            }
+        } else if (event->key() == Qt::Key_Backspace) {
+            if (!currentInput.isEmpty()) {
+                currentInput.chop(1);
+                setProperty("dimensionInput", currentInput);
+                update();
+                return;
+            }
+        } else if (event->key() == Qt::Key_Return || event->key() == Qt::Key_Enter) {
+            bool ok;
+            double length = currentInput.toDouble(&ok);
+            if (ok && length > 0) {
+                QVector3D worldPos = unproject(m_currentMousePos, m_currentPlane);
+                QVector3D startPos(m_firstLinePoint.X(), m_firstLinePoint.Y(), m_firstLinePoint.Z());
+                QVector3D dir = (worldPos - startPos);
+                if (dir.length() > 1e-6) {
+                    dir.normalize();
+                    QVector3D endPos = startPos + length * dir;
+                    gp_Pnt p;
+                    p.SetCoord(endPos.x(), endPos.y(), endPos.z());
+                    emit lineAdded(m_firstLinePoint, p);
+                    m_firstLinePoint = p; // for chained lines
+                    setProperty("dimensionInput", QVariant(""));
+                    update();
+                    return;
+                }
+            }
+        }
+    }
+
     if (event->key() == Qt::Key_Escape) {
         if (m_isDefiningLine) {
             m_isDefiningLine = false;
+            setProperty("dimensionInput", QVariant(""));
             emit toolDeactivated();
             update();
             return;