diff --git a/app/src/main/java/at/florianschuster/hydro/ui/CupCarouselSelection.kt b/app/src/main/java/at/florianschuster/hydro/ui/CupCarouselSelection.kt
index f1b3fac..ac7e192 100644
--- a/app/src/main/java/at/florianschuster/hydro/ui/CupCarouselSelection.kt
+++ b/app/src/main/java/at/florianschuster/hydro/ui/CupCarouselSelection.kt
@@ -1,25 +1,36 @@
 package at.florianschuster.hydro.ui
 
+import androidx.compose.foundation.clickable
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.PaddingValues
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.text.KeyboardOptions
 import androidx.compose.material3.AlertDialog
 import androidx.compose.material3.Button
+import androidx.compose.material3.CardDefaults
+import androidx.compose.material3.Icon
 import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.OutlinedCard
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.text.input.KeyboardType
 import androidx.compose.ui.unit.dp
 import at.florianschuster.hydro.AppAction
 import at.florianschuster.hydro.AppState
 import at.florianschuster.hydro.model.Cup
+import at.florianschuster.hydro.model.Milliliters
+import at.florianschuster.hydro.model.icon
 import at.florianschuster.hydro.ui.base.HydrationCarousel
+import at.florianschuster.hydro.model.LiquidUnit
 
 @Composable
 fun CupCarouselSelection(
@@ -61,6 +72,50 @@ fun CupCarouselSelection(
                 } else {
                     dispatch(AppAction.SetSelectedCups(state.selectedCups + cup))
                 }
+            },
+            trailingContent = {
+                var showCustomDialog by remember { mutableStateOf(false) }
+
+                OutlinedCard(
+                    modifier = Modifier.clickable { showCustomDialog = true },
+                    colors = CardDefaults.outlinedCardColors(
+                        containerColor = MaterialTheme.colorScheme.surface
+                    ),
+                    border = CardDefaults.outlinedCardBorder(false)
+                ) {
+                    Column(
+                        modifier = Modifier.padding(16.dp),
+                        horizontalAlignment = Alignment.CenterHorizontally
+                    ) {
+                        Icon(
+                            modifier = Modifier.size(28.dp),
+                            painter = Milliliters(500).icon(),
+                            contentDescription = null
+                        )
+                        Text("Custom…", style = MaterialTheme.typography.labelLarge)
+                    }
+                }
+
+                if (showCustomDialog) {
+                    CustomSizeDialog(
+                        liquidUnit = state.liquidUnit,
+                        onConfirm = { ml ->
+                            showCustomDialog = false
+                            val bounded = ml.coerceIn(50, 5000)
+                            if (state.selectedCups.any { it.milliliters == Milliliters(bounded) }) return@CustomSizeDialog
+                            if (state.selectedCups.size >= 3) {
+                                showCanOnlySelectThreeAlert = true
+                            } else {
+                                dispatch(
+                                    AppAction.SetSelectedCups(
+                                        state.selectedCups + Cup(milliliters = Milliliters(bounded))
+                                    )
+                                )
+                            }
+                        },
+                        onDismiss = { showCustomDialog = false }
+                    )
+                }
             }
         )
         if (showCanOnlySelectThreeAlert) {
@@ -78,3 +133,62 @@ fun CupCarouselSelection(
         }
     }
 }
+@Composable
+private fun CustomSizeDialog(
+    liquidUnit: LiquidUnit,
+    onConfirm: (Int /* ml */) -> Unit,
+    onDismiss: () -> Unit,
+) {
+    val (unitLabel, toMlFactor, minMl) = when (liquidUnit) {
+        LiquidUnit.Milliliter   -> Triple("ml", 1.0, 50)
+        LiquidUnit.USFluidOunce -> Triple("fl oz (US)", 29.5735, 1)
+        LiquidUnit.UKFluidOunce -> Triple("fl oz (UK)", 28.4131, 1)
+    }
+    val maxMl = 5000
+    val minDisplay = (minMl / toMlFactor).coerceAtLeast(1.0).toInt()
+    val maxDisplay = (maxMl / toMlFactor).toInt()
+
+    var text by remember { mutableStateOf("") }
+    val sanitized = remember(text) {
+        text.replace(',', '.')
+            .filterIndexed { i, c -> c.isDigit() || (c == '.' && !text.take(i).contains('.')) }
+    }
+    val entered = sanitized.toDoubleOrNull()
+    val ml = entered?.let { (it * toMlFactor).toInt() }
+    val valid = ml != null && ml in minMl..maxMl
+
+    AlertDialog(
+        onDismissRequest = onDismiss,
+        title = { Text("Custom size") },
+        text = {
+            Column {
+                androidx.compose.material3.OutlinedTextField(
+                    value = text,
+                    onValueChange = { text = it },
+                    label = { Text("Amount") },
+                    placeholder = { Text(if (liquidUnit == LiquidUnit.Milliliter) "500" else "16") },
+                    singleLine = true,
+                    keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Decimal),
+                    suffix = { Text(unitLabel) },
+                    isError = !valid && text.isNotEmpty()
+                )
+                Spacer(Modifier.height(4.dp))
+                Text(
+                    if (valid && ml != null) "≈ $ml ml"
+                    else "Enter a value between $minDisplay–$maxDisplay $unitLabel",
+                    color = if (valid || text.isEmpty())
+                        MaterialTheme.colorScheme.onSurfaceVariant
+                    else
+                        MaterialTheme.colorScheme.error,
+                    style = MaterialTheme.typography.bodySmall
+                )
+            }
+        },
+        confirmButton = {
+            Button(enabled = valid, onClick = { onConfirm(ml!!) }) { Text("OK") }
+        },
+        dismissButton = {
+            androidx.compose.material3.TextButton(onClick = onDismiss) { Text("Cancel") }
+        }
+    )
+}
\ No newline at end of file
diff --git a/app/src/main/java/at/florianschuster/hydro/ui/base/HydrationCarousel.kt b/app/src/main/java/at/florianschuster/hydro/ui/base/HydrationCarousel.kt
index fbf2d1a..87d5d5b 100644
--- a/app/src/main/java/at/florianschuster/hydro/ui/base/HydrationCarousel.kt
+++ b/app/src/main/java/at/florianschuster/hydro/ui/base/HydrationCarousel.kt
@@ -32,7 +32,8 @@ fun HydrationCarousel(
     liquidUnit: LiquidUnit,
     selected: List<Milliliters> = emptyList(),
     onClick: (index: Int, Milliliters) -> Unit = { _, _ -> },
-    contentBelowItem: @Composable (index: Int) -> Unit = {}
+    contentBelowItem: @Composable (index: Int) -> Unit = {},
+    trailingContent: @Composable () -> Unit = {}
 ) {
     LazyRow(
         modifier = modifier,
@@ -49,6 +50,7 @@ fun HydrationCarousel(
                 contentBelowItem = contentBelowItem
             )
         }
+        item { trailingContent() }
     }
 }