diff --git a/format.go b/format.go
index de77992..3693259 100644
--- a/format.go
+++ b/format.go
@@ -1,9 +1,6 @@
 package mpb
 
-import (
-	"fmt"
-	"strings"
-)
+import "fmt"
 
 const (
 	_          = iota
@@ -16,7 +13,7 @@
 type Units uint
 
 const (
-	UnitNone Units = iota
+	_ = iota
 	UnitBytes
 )
 
@@ -51,17 +48,16 @@
 
 func formatBytes(i int64) (result string) {
 	switch {
-	case i > bytesInTiB:
+	case i >= bytesInTiB:
 		result = fmt.Sprintf("%.1fTiB", float64(i)/bytesInTiB)
-	case i > bytesInGiB:
+	case i >= bytesInGiB:
 		result = fmt.Sprintf("%.1fGiB", float64(i)/bytesInGiB)
-	case i > bytesInMiB:
+	case i >= bytesInMiB:
 		result = fmt.Sprintf("%.1fMiB", float64(i)/bytesInMiB)
-	case i > bytesInKiB:
+	case i >= bytesInKiB:
 		result = fmt.Sprintf("%.1fKiB", float64(i)/bytesInKiB)
 	default:
 		result = fmt.Sprintf("%db", i)
 	}
-	result = strings.Trim(result, " ")
 	return
 }
diff --git a/format_test.go b/format_test.go
new file mode 100644
index 0000000..7529b62
--- /dev/null
+++ b/format_test.go
@@ -0,0 +1,51 @@
+package mpb_test
+
+import (
+	"testing"
+
+	"github.com/vbauerster/mpb"
+)
+
+const (
+	_   = iota
+	KiB = 1 << (iota * 10)
+	MiB
+	GiB
+	TiB
+)
+
+func TestFormatNoUnits(t *testing.T) {
+	actual := mpb.Format(1234567).String()
+	expected := "1234567"
+	if actual != expected {
+		t.Errorf("Expected %q but found %q", expected, actual)
+	}
+}
+
+func TestFormatWidth(t *testing.T) {
+	actual := mpb.Format(1234567).Width(10).String()
+	expected := "   1234567"
+	if actual != expected {
+		t.Errorf("Expected %q but found %q", expected, actual)
+	}
+}
+
+func TestFormatToBytes(t *testing.T) {
+	inputs := []struct {
+		v int64
+		e string
+	}{
+		{v: 1000, e: "1000b"},
+		{v: 1024, e: "1.0KiB"},
+		{v: 3*MiB + 140*KiB, e: "3.1MiB"},
+		{v: 2 * GiB, e: "2.0GiB"},
+		{v: 4 * TiB, e: "4.0TiB"},
+	}
+
+	for _, input := range inputs {
+		actual := mpb.Format(input.v).To(mpb.UnitBytes).String()
+		if actual != input.e {
+			t.Errorf("Expected %q but found %q", input.e, actual)
+		}
+	}
+}