diff --git a/table/render.go b/table/render.go
index bb8dad5..dadfa53 100644
--- a/table/render.go
+++ b/table/render.go
@@ -50,7 +50,7 @@ func (t *Table) Render() string {
 }
 
 func (t *Table) renderColumn(out *strings.Builder, row rowStr, colIdx int, maxColumnLength int, hint renderHint) int {
-	numColumnsRenderer := 1
+	numColumnsRendered := 1
 
 	// when working on the first column, and autoIndex is true, insert a new
 	// column with the row number on it.
@@ -84,10 +84,8 @@ func (t *Table) renderColumn(out *strings.Builder, row rowStr, colIdx int, maxCo
 				break
 			}
 			align = text.AlignCenter
-			maxColumnLength += t.maxColumnLengths[idx] +
-				text.RuneCount(t.style.Box.PaddingRight+t.style.Box.PaddingLeft) +
-				1
-			numColumnsRenderer++
+			maxColumnLength += t.getMaxColumnLengthForMerging(idx)
+			numColumnsRendered++
 		}
 	}
 	colStr = align.Apply(colStr, maxColumnLength)
@@ -99,7 +97,7 @@ func (t *Table) renderColumn(out *strings.Builder, row rowStr, colIdx int, maxCo
 
 	t.renderColumnColorized(out, colIdx, colStr, hint)
 
-	return colIdx + numColumnsRenderer
+	return colIdx + numColumnsRendered
 }
 
 func (t *Table) renderColumnAutoIndex(out *strings.Builder, hint renderHint) {
diff --git a/table/render_html_test.go b/table/render_html_test.go
index 8bebbf5..5d9b69c 100644
--- a/table/render_html_test.go
+++ b/table/render_html_test.go
@@ -2,7 +2,6 @@ package table
 
 import (
 	"fmt"
-	"os"
 	"testing"
 
 	"github.com/jedib0t/go-pretty/v6/text"
@@ -99,7 +98,7 @@ func TestTable_RenderHTML_AutoIndex(t *testing.T) {
 		}
 		tw.AppendFooter(row)
 	}
-	tw.SetOutputMirror(os.Stdout)
+	tw.SetOutputMirror(nil)
 	tw.SetAutoIndex(true)
 	tw.SetStyle(StyleLight)
 
@@ -251,7 +250,7 @@ func TestTable_RenderHTML_CustomStyle(t *testing.T) {
 		EscapeText:  false,
 		Newline:     "<!-- newline -->",
 	}
-	tw.SetOutputMirror(os.Stdout)
+	tw.SetOutputMirror(nil)
 
 	expectedOut := `<table class="game-of-thrones">
   <thead>
diff --git a/table/render_test.go b/table/render_test.go
index 23a36e8..b8a967d 100644
--- a/table/render_test.go
+++ b/table/render_test.go
@@ -210,7 +210,8 @@ func TestTable_Render_AutoMerge_Complex(t *testing.T) {
 │   │                              │           ├─────┴─────┼─────┤
 │   │                              │           │     5     │     │
 └───┴──────────────────────────────┴───────────┴───────────┴─────┘`
-	assert.Equal(t, expectedOut, tw.Render())
+	out := tw.Render()
+	assert.Equal(t, expectedOut, out)
 }
 
 func TestTable_Render_AutoMerge_Complex2(t *testing.T) {
diff --git a/table/table.go b/table/table.go
index ae11c32..eadf9b7 100644
--- a/table/table.go
+++ b/table/table.go
@@ -548,6 +548,15 @@ func (t *Table) getFormat(hint renderHint) text.Format {
 	return t.style.Format.Row
 }
 
+func (t *Table) getMaxColumnLengthForMerging(colIdx int) int {
+	maxColumnLength := t.maxColumnLengths[colIdx]
+	maxColumnLength += text.RuneCount(t.style.Box.PaddingRight + t.style.Box.PaddingLeft)
+	if t.style.Options.SeparateColumns {
+		maxColumnLength += text.RuneCount(t.style.Box.EmptySeparator)
+	}
+	return maxColumnLength
+}
+
 func (t *Table) getRow(rowIdx int, hint renderHint) rowStr {
 	switch {
 	case hint.isHeaderRow: