diff --git a/public/video.html b/public/video.html
index 4e92ad1..08c1229 100644
--- a/public/video.html
+++ b/public/video.html
@@ -740,10 +740,12 @@
     // ─── Estimate sizes for compress mode ─────────────────────────────────────
     function updateEstimates() {
         if (!state.originalSize) return;
-        const ratios = { high: 0.70, medium: 0.40, low: 0.20 };
-        for (const [q, ratio] of Object.entries(ratios)) {
-            const el = document.getElementById('est-' + q);
-            if (el) el.textContent = '~' + formatSize(state.originalSize * ratio);
+        var formatMult = { mp4: 1.0, avi: 1.35, mkv: 1.05 };
+        var fm = formatMult[state.compressFormat || 'mp4'] || 1.0;
+        var ratios = { high: 0.70, medium: 0.40, low: 0.20 };
+        for (var q in ratios) {
+            var el = document.getElementById('est-' + q);
+            if (el) el.textContent = '~' + formatSize(state.originalSize * ratios[q] * fm);
         }
     }
 
@@ -910,7 +912,7 @@
 
     initBtnGroup('convertFormats', val => { state.format = val; });
     initBtnGroup('audioFormats',   val => { state.audioFormat = val; });
-    initBtnGroup('compressFormats', val => { state.compressFormat = val; });
+    initBtnGroup('compressFormats', val => { state.compressFormat = val; updateEstimates(); });
 
     // ─── Quality options ───────────────────────────────────────────────────────
     document.querySelectorAll('.quality-option').forEach(label => {