diff --git a/changelog.txt b/changelog.txt
index 2dba3fe7f..d4a195bcd 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -1,5 +1,5 @@
 V1.XX.X
-[QMS-902] Add basic HiDPI support
+[QMS-902] Add HiDPI support
 [QMS-963] Add action to move a map to the top in map list
 [QMS-1105] Fix: Context menu shortcuts not shown (macOS)
 [QMS-1111] Add percentage values to track range
diff --git a/src/qmapshack/canvas/IDrawContext.cpp b/src/qmapshack/canvas/IDrawContext.cpp
index 9d39be727..6a6aeb1d1 100644
--- a/src/qmapshack/canvas/IDrawContext.cpp
+++ b/src/qmapshack/canvas/IDrawContext.cpp
@@ -423,7 +423,6 @@ void IDrawContext::run() {
     // map render objects to buffer structure
     currentBuffer.zoomFactor = zoomFactor;
     currentBuffer.scale = scale;
-    currentBuffer.pixelRatio = pixelRatio;
     currentBuffer.ref1 = ref1;
     currentBuffer.ref2 = ref2;
     currentBuffer.ref3 = ref3;
diff --git a/src/qmapshack/canvas/IDrawContext.h b/src/qmapshack/canvas/IDrawContext.h
index 2c4e84f59..80404a991 100644
--- a/src/qmapshack/canvas/IDrawContext.h
+++ b/src/qmapshack/canvas/IDrawContext.h
@@ -43,7 +43,6 @@ class IDrawContext : public QThread {
     int zoomLevels;                //< the number of zoom levels
     QPointF zoomFactor{1.0, 1.0};  //< the zoomfactor used to draw the canvas
     QPointF scale{1.0, 1.0};       //< the scale of the global viewport
-    qreal pixelRatio = 1.0;        //< device pixel ratio of the canvas
 
     QPointF ref1;   //< top left corner
     QPointF ref2;   //< top right corner
diff --git a/src/qmapshack/canvas/IDrawObject.cpp b/src/qmapshack/canvas/IDrawObject.cpp
index 2397ec36b..26e38c19e 100644
--- a/src/qmapshack/canvas/IDrawObject.cpp
+++ b/src/qmapshack/canvas/IDrawObject.cpp
@@ -99,7 +99,8 @@ void IDrawObject::drawTileLQ(const QImage& img, QPolygonF& l, QPainter& p, IDraw
   // finally translate, scale, rotate and draw tile
   p.save();
   p.translate(l[0]);
-  p.scale(w / img.width(), h / img.height());
+  auto imgSize = img.deviceIndependentSize();
+  p.scale(w / imgSize.width(), h / imgSize.height());
   p.rotate(a);
   p.drawImage(0, 0, img);
   p.restore();
@@ -107,15 +108,16 @@ void IDrawObject::drawTileLQ(const QImage& img, QPolygonF& l, QPainter& p, IDraw
 
 void IDrawObject::drawTileHQ(const QImage& img, QPolygonF& l, QPainter& p, IDrawContext& context,
                              const CProj& proj) const {
+  auto imgSize = img.deviceIndependentSize();
   // the sub-tiles need a sensible size
   // if they get too small there will be too much
   // rounding effects.
   qint32 nStepsX = 8;
   qint32 nStepsY = 8;
-  if (img.width() / nStepsX < 32) {
+  if (imgSize.width() / nStepsX < 32) {
     nStepsX = 4;
   }
-  if (img.height() / nStepsY < 32) {
+  if (imgSize.height() / nStepsY < 32) {
     nStepsY = 4;
   }
 
@@ -161,7 +163,7 @@ void IDrawObject::drawTileHQ(const QImage& img, QPolygonF& l, QPainter& p, IDraw
   // canvas using the view's projection
   context.convertRad2Px(quads);
 
-  QRectF rect(0, 0, img.width() / nStepsX, img.height() / nStepsY);
+  QRectF rect(0, 0, imgSize.width() / nStepsX, imgSize.height() / nStepsY);
   const qreal rw = rect.width();
   const qreal rh = rect.height();
 
diff --git a/src/qmapshack/dem/CDemVRT.cpp b/src/qmapshack/dem/CDemVRT.cpp
index c1e03066d..9dd1a48f0 100644
--- a/src/qmapshack/dem/CDemVRT.cpp
+++ b/src/qmapshack/dem/CDemVRT.cpp
@@ -325,8 +325,8 @@ void CDemVRT::draw(IDrawContext::buffer_t& buf) {
   }
 
   // use bufferScale (and therefore the zoom level) and the pixel scale of the DEM to caluclate a downsampling factor
-  qreal buf_scale_x = qAbs(bufferScale.x() / xscale);
-  qreal buf_scale_y = qAbs(bufferScale.y() / yscale);
+  qreal buf_scale_x = qAbs(bufferScale.x() / xscale / buf.image.devicePixelRatio());
+  qreal buf_scale_y = qAbs(bufferScale.y() / yscale / buf.image.devicePixelRatio());
   // <1 would mean GDAL does upscaling which is pointless
   if (buf_scale_x < 1.0) {
     buf_scale_x = 1.0;
diff --git a/src/qmapshack/map/CMapGEMF.cpp b/src/qmapshack/map/CMapGEMF.cpp
index 0afb07ded..a994992c8 100644
--- a/src/qmapshack/map/CMapGEMF.cpp
+++ b/src/qmapshack/map/CMapGEMF.cpp
@@ -161,7 +161,7 @@ void CMapGEMF::draw(IDrawContext::buffer_t& buf) {
     x2 = 180 * DEG_TO_RAD;
   }
 
-  QPointF s1 = buf.scale * buf.zoomFactor / buf.pixelRatio;
+  QPointF s1 = buf.scale * buf.zoomFactor;
   qreal d = NOFLOAT;
   quint32 z = MAX_ZOOM_LEVEL;
 
diff --git a/src/qmapshack/map/CMapJNX.cpp b/src/qmapshack/map/CMapJNX.cpp
index 9ea0b2f04..5a7df01da 100644
--- a/src/qmapshack/map/CMapJNX.cpp
+++ b/src/qmapshack/map/CMapJNX.cpp
@@ -287,7 +287,7 @@ void CMapJNX::draw(IDrawContext::buffer_t& buf) /* override */
       break;
     }
 
-    qint32 level = scale2level(bufferScale.x() / (5 * buf.pixelRatio), mapFile);
+    qint32 level = scale2level(bufferScale.x() / 5, mapFile);
 
     // no scalable level found, draw bounding box of map
     // derive maps corner coordinate
diff --git a/src/qmapshack/map/CMapRMAP.cpp b/src/qmapshack/map/CMapRMAP.cpp
index 0d5968583..755c0d868 100644
--- a/src/qmapshack/map/CMapRMAP.cpp
+++ b/src/qmapshack/map/CMapRMAP.cpp
@@ -343,7 +343,7 @@ void CMapRMAP::draw(IDrawContext::buffer_t& buf) /* override */
     return;
   }
 
-  level_t& level = findBestLevel(bufferScale / buf.pixelRatio);
+  level_t& level = findBestLevel(bufferScale);
 
   // convert top left and bottom right point of buffer to local coord. system
   QPointF p1 = buf.ref1;
diff --git a/src/qmapshack/map/CMapTMS.cpp b/src/qmapshack/map/CMapTMS.cpp
index dd328270d..a87d5df55 100644
--- a/src/qmapshack/map/CMapTMS.cpp
+++ b/src/qmapshack/map/CMapTMS.cpp
@@ -28,21 +28,45 @@
 #include "helpers/CDraw.h"
 #include "map/CMapDraw.h"
 #include "map/cache/CDiskCache.h"
-#include "units/IUnit.h"
 
-inline int lon2tile(double lon, int z) { return (int)(qRound(256 * (lon + 180.0) / 360.0 * qPow(2.0, z))); }
-
-inline int lat2tile(double lat, int z) {
-  return (int)(qRound(256 * (1.0 - log(qTan(lat * M_PI / 180.0) + 1.0 / qCos(lat * M_PI / 180.0)) / M_PI) / 2.0 *
-                      qPow(2.0, z)));
-}
-
-inline double tile2lon(int x, int z) { return x / qPow(2.0, z) * 360.0 - 180; }
-
-inline double tile2lat(int y, int z) {
-  double n = M_PI - 2.0 * M_PI * y / qPow(2.0, z);
-  return 180.0 / M_PI * qAtan(0.5 * (exp(n) - exp(-n)));
-}
+namespace {
+// extend of web mercator per direction in (projected) meters
+// meaning the web mercator projection goes from -C to +C in both axis
+constexpr qreal C = 20037508.34;
+
+// convert from web mercator meters to tile indices
+QPoint toTile(const QPointF& p, int z) {
+  int n = (1 << z);  // n tiles across the map
+  // normalize into [0,1]
+  qreal x = (1 + p.x() / C) / 2;
+  qreal y = (1 - p.y() / C) / 2;
+
+  // tile that contains p
+  int x_tile = x * n;
+  int y_tile = y * n;
+  // clamp to valid range
+  x_tile = std::clamp(x_tile, 0, n - 1);
+  y_tile = std::clamp(y_tile, 0, n - 1);
+
+  return QPoint(x_tile, y_tile);
+};
+
+// get web mercator meters for the NW corner of a tile
+QPointF fromTile(const QPoint& p, int z) {
+  int n = (1 << z);
+  // get normalized again
+  qreal x = static_cast<qreal>(p.x()) / n;
+  qreal y = static_cast<qreal>(p.y()) / n;
+
+  return QPointF((2 * x - 1) * C, (2 * y - 1) * -C);
+};
+
+// euclidian modulo
+int eucmod(int a, int b) {
+  int r = a % b;
+  return r >= 0 ? r : r + std::abs(b);
+};
+}  // namespace
 
 CMapTMS::CMapTMS(const QString& filename, CMapDraw* parent) : IMapOnline(parent) {
   qDebug() << "------------------------------";
@@ -106,6 +130,7 @@ CMapTMS::CMapTMS(const QString& filename, CMapDraw* parent) : IMapOnline(parent)
     layers[idx].script = xmlLayer.namedItem("Script").toElement().text();
     layers[idx].minZoomLevel = minZoomLevel;
     layers[idx].maxZoomLevel = maxZoomLevel;
+    layers[idx].tileSizePx = 256;
 
     layers[idx].strUrl.replace("{z}", "%1", Qt::CaseInsensitive);
     layers[idx].strUrl.replace("{x}", "%2", Qt::CaseInsensitive);
@@ -293,89 +318,72 @@ void CMapTMS::draw(IDrawContext::buffer_t& buf) /* override */
     return;
   }
 
-  // get pixel offset of top left buffer corner
-  QPointF pp = buf.ref1;
-  map->convertRad2Px(pp);
+  // get the top-left and bottom-right corners into web mercator
+  auto r1 = buf.ref1;
+  auto r3 = buf.ref3;
+  proj.transform(r1, PJ_INV);
+  proj.transform(r3, PJ_INV);
+  QPointF pt1(r1.x(), r1.y());
+  QPointF pt2(r3.x(), r3.y());
 
   // start to draw the map
   QPainter p(&buf.image);
   USE_ANTI_ALIASING(p, true);
   p.setOpacity(getOpacity() / 100.0);
+  QPointF pp = buf.ref1;
+  map->convertRad2Px(pp);
   p.translate(-pp);
 
-  // calculate maximum viewport
-  qreal x1 = buf.ref1.x() < buf.ref4.x() ? buf.ref1.x() : buf.ref4.x();
-  qreal y1 = buf.ref1.y() > buf.ref2.y() ? buf.ref1.y() : buf.ref2.y();
-
-  qreal x2 = buf.ref2.x() > buf.ref3.x() ? buf.ref2.x() : buf.ref3.x();
-  qreal y2 = buf.ref3.y() < buf.ref4.y() ? buf.ref3.y() : buf.ref4.y();
-
-  if (x1 < -180.0 * DEG_TO_RAD) {
-    x1 = -180 * DEG_TO_RAD;
-  }
-  if (x2 > 180.0 * DEG_TO_RAD) {
-    x2 = 180 * DEG_TO_RAD;
-  }
-
-  // draw layers
-  for (const layer_t& layer : std::as_const(layers)) {
+  for (auto& layer : layers) {
     if (!layer.enabled) {
       continue;
     }
 
-    qint32 z = 20;
-    QPointF s1 = buf.scale * buf.zoomFactor / buf.pixelRatio;
-    qreal d = NOFLOAT;
-
-    for (qint32 i = layer.minZoomLevel; i < 21; i++) {
-      qreal s2 = 0.055 * (1 << i);
-      if (qAbs(s2 - s1.x()) < d) {
-        z = i;
-        d = qAbs(s2 - s1.x());
-      }
-    }
-
+    // calculate zoom level
+    qreal width = std::remainder(pt2.x() - pt1.x(), C);
+    qint32 z = std::round(std::log2(2 * C / (width / buf.image.width() * layer.tileSizePx)));
+    z = qMax(z, layer.minZoomLevel);
     if (z > layer.maxZoomLevel) {
       continue;
     }
+    int n = (1 << z);
 
-    z = 21 - z;
-
-    qint32 row1, row2, col1, col2;
+    // tile indices of the two corners and number of tiles between them
+    auto t1 = toTile(pt1, z);
+    auto t2 = toTile(pt2, z);
+    auto dim = t2 - t1;
+    dim = {eucmod(dim.x(), n), dim.y()};
 
-    col1 = lon2tile(x1 * RAD_TO_DEG, z) / 256;
-    col2 = lon2tile(x2 * RAD_TO_DEG, z) / 256;
-    row1 = lat2tile(y1 * RAD_TO_DEG, z) / 256;
-    row2 = lat2tile(y2 * RAD_TO_DEG, z) / 256;
-
-    //        qDebug() << col1 << col2 << row1 << row2 << (col2 - col1) << (row2 - row1) << ((col2 - col1) * (row2 -
-    //        row1));
-
-    // start to request tiles. draw tiles in cache, queue urls of tile yet to be requested
-    for (qint32 row = row1; row <= row2; row++) {
-      for (qint32 col = col1; col <= col2; col++) {
-        QString url = createUrl(layer, col, row, z);
-        //                qDebug() << url;
+    for (int i = 0; i <= dim.y(); ++i) {
+      for (int j = 0; j <= dim.x(); ++j) {
+        int x = eucmod(t1.x() + j, n);
+        int y = t1.y() + i;
+        QString url = createUrl(layer, x, y, z);
 
         if (diskCache->contains(url)) {
           QImage img;
           diskCache->restore(url, img);
-
+          img.setDevicePixelRatio(buf.image.devicePixelRatio());
+          if (img.width() != layer.tileSizePx) {
+            // we got a tile with a different size then expected
+            // (which is normal for the first tile we get from e.g. a HiDPI source)
+            // remember it's size and request a redraw
+            layer.tileSizePx = img.width();
+            map->emitSigCanvasUpdate();
+          }
+
+          // TODO throw away drawTile and handle drawing in a sane way
+          // then we'll also get wraparound on the antimeridian
+          // (this function is ready but it's impossible with drawTile)
           QPolygonF l;
-
-          qreal xx1 = tile2lon(col, z) * DEG_TO_RAD;
-          qreal yy1 = tile2lat(row, z) * DEG_TO_RAD;
-          qreal xx2 = tile2lon(col + 1, z) * DEG_TO_RAD;
-          qreal yy2 = tile2lat(row + 1, z) * DEG_TO_RAD;
-
-          l << QPointF(xx1, yy1) << QPointF(xx2, yy1) << QPointF(xx2, yy2) << QPointF(xx1, yy2);
+          l << fromTile({x, y}, z) << fromTile({x + 1, y}, z) << fromTile({x + 1, y + 1}, z) << fromTile({x, y + 1}, z);
+          proj.transform(l, PJ_FWD);
           drawTile(img, l, p);
         } else {
           urlQueue << url;
         }
       }
     }
-
     emit sigQueueChanged();
   }
 }
diff --git a/src/qmapshack/map/CMapTMS.h b/src/qmapshack/map/CMapTMS.h
index e0e850c88..472c5714f 100644
--- a/src/qmapshack/map/CMapTMS.h
+++ b/src/qmapshack/map/CMapTMS.h
@@ -47,10 +47,11 @@ class CMapTMS : public IMapOnline {
   QString createUrl(const layer_t& layer, int x, int y, int z);
 
   struct layer_t {
-    layer_t() : enabled(true), minZoomLevel(0), maxZoomLevel(0) {}
+    layer_t() : enabled(true), minZoomLevel(0), maxZoomLevel(0), tileSizePx(256) {}
     bool enabled;
     qint32 minZoomLevel;
     qint32 maxZoomLevel;
+    qint32 tileSizePx;
     QString title;
     QString strUrl;
     QString script;
diff --git a/src/qmapshack/map/CMapVRT.cpp b/src/qmapshack/map/CMapVRT.cpp
index c0c1ebdcc..0257a1460 100644
--- a/src/qmapshack/map/CMapVRT.cpp
+++ b/src/qmapshack/map/CMapVRT.cpp
@@ -282,8 +282,8 @@ bool CMapVRT::computeSourceWindow(const IDrawContext::buffer_t& buf, const QPoin
                                   sourceWindow_t& window) const {
   // use bufferScale (and therefore the zoom level) and the pixel scale of the map to calculate a downsampling
   // factor; <1 would mean GDAL does upscaling which is pointless
-  window.bufScaleX = qMax(1.0, qAbs(bufferScale.x() / xscale));
-  window.bufScaleY = qMax(1.0, qAbs(bufferScale.y() / yscale));
+  window.bufScaleX = qMax(1.0, qAbs(bufferScale.x() / xscale) / buf.image.devicePixelRatio());
+  window.bufScaleY = qMax(1.0, qAbs(bufferScale.y() / yscale) / buf.image.devicePixelRatio());
 
   // corners of the area we shall draw, converted from the canvas projection into the
   // map's own pixel coordinate space
diff --git a/src/qmapshack/map/CMapWMTS.cpp b/src/qmapshack/map/CMapWMTS.cpp
index ebdaea091..40ca6fcd7 100644
--- a/src/qmapshack/map/CMapWMTS.cpp
+++ b/src/qmapshack/map/CMapWMTS.cpp
@@ -383,7 +383,7 @@ void CMapWMTS::draw(IDrawContext::buffer_t& buf) /* override */
   QRectF viewport(QPointF(x1, y1) * RAD_TO_DEG, QPointF(x2, y2) * RAD_TO_DEG);
 
   // draw layers
-  for (const layer_t& layer : std::as_const(layers)) {
+  for (layer_t& layer : layers) {
     if (!layer.boundingBox.intersects(viewport) || !layer.enabled) {
       continue;
     }
@@ -410,7 +410,12 @@ void CMapWMTS::draw(IDrawContext::buffer_t& buf) /* override */
     const QStringList& keys = tileset.tilematrix.keys();
     for (const QString& key : keys) {
       const tilematrix_t& tilematrix = tileset.tilematrix[key];
-      qreal s2 = tilematrix.scale * 0.28e-3;
+      // Effective ground resolution of a served tile pixel. For spec-compliant
+      // layers tileScale is 1.0 and this is just the declared pixel span. For
+      // HiDPI servers that serve tiles larger than their TileMatrixSet declares,
+      // dividing by tileScale selects a coarser matrix so the bigger tile still
+      // maps 1:1 onto the (physical) buffer pixels.
+      qreal s2 = tilematrix.scale * 0.28e-3 / layer.tileScale;
 
       if (qAbs(s2 - s1.x()) < d) {
         tileMatrixId = key;
@@ -486,6 +491,16 @@ void CMapWMTS::draw(IDrawContext::buffer_t& buf) /* override */
           QImage img;
           diskCache->restore(url, img);
 
+          // Detect HiDPI servers that serve tiles larger (or smaller) than the
+          // TileWidth declared in their TileMatrixSet. Learn the real ratio from
+          // the fetched tile and request a redraw so a matching matrix is picked
+          // and the tile is drawn 1:1 to physical pixels (sharp, with the HiDPI
+          // text-size advantage on scaled displays).
+          if (tilematrix.tileWidth > 0 && img.width() != qRound(tilematrix.tileWidth * layer.tileScale)) {
+            layer.tileScale = qreal(img.width()) / tilematrix.tileWidth;
+            map->emitSigCanvasUpdate();
+          }
+
           QPolygonF l;
 
           qreal xx1 = col * (xscale * tilematrix.tileWidth) + tilematrix.topLeft.x();
diff --git a/src/qmapshack/map/CMapWMTS.h b/src/qmapshack/map/CMapWMTS.h
index 09506cd6f..cfc3b770d 100644
--- a/src/qmapshack/map/CMapWMTS.h
+++ b/src/qmapshack/map/CMapWMTS.h
@@ -60,6 +60,16 @@ class CMapWMTS : public IMapOnline {
     QRectF boundingBox;
     QString resourceURL;
     QMap<QString, limit_t> limits;
+
+    /**
+       Ratio of the actually served tile size to the TileWidth declared in the
+       TileMatrixSet. Some HiDPI servers violate the WMTS spec by reusing a
+       standard TileMatrixSet (e.g. TileWidth 256) while serving larger tiles
+       (e.g. 512px). The ratio is learned from the first fetched tile and used
+       to pick a matching (coarser) matrix so an over-sized tile still maps 1:1
+       onto the physical buffer pixels. 1.0 means the server is spec-compliant.
+     */
+    qreal tileScale = 1.0;
   };
 
   QList<layer_t> layers;