diff --git a/drivers/include/mq3.h b/drivers/include/mq3.h
index cac5b135ef..fac2275fb6 100644
--- a/drivers/include/mq3.h
+++ b/drivers/include/mq3.h
@@ -50,8 +50,8 @@ typedef struct {
  * @param[out] dev      device descriptor of an MQ-3 sensor
  * @param[in] adc_line  the ADC device the sensor is connected to
  *
- * @return              0 on success
- * @return              -1 on error
+ * @retval  0       success
+ * @retval  -1      failure
  */
 int mq3_init(mq3_t *dev, adc_t adc_line);
 
@@ -62,7 +62,7 @@ int mq3_init(mq3_t *dev, adc_t adc_line);
  *
  * @return              the raw sensor value, between 0 and MQ3_MAX_RAW_VALUE
  */
-int mq3_read_raw(const mq3_t *dev);
+int16_t mq3_read_raw(const mq3_t *dev);
 
 /**
  * @brief   Read the scaled sensor value of PPM of alcohol
@@ -71,7 +71,7 @@ int mq3_read_raw(const mq3_t *dev);
  *
  * @return              the scaled sensor value in PPM of alcohol
  */
-int mq3_read(const mq3_t *dev);
+int16_t mq3_read(const mq3_t *dev);
 
 #ifdef __cplusplus
 }
diff --git a/drivers/mq3/mq3.c b/drivers/mq3/mq3.c
index d89f92564e..a3f28ed854 100644
--- a/drivers/mq3/mq3.c
+++ b/drivers/mq3/mq3.c
@@ -19,10 +19,14 @@
  */
 
 #include "mq3.h"
+#include "macros/math.h"
 
 #define PRECISION           ADC_RES_10BIT
-#define MIN                 (100U)              /* TODO: calibrate to useful value */
-#define FACTOR              (2.33f)             /* TODO: calibrate to useful value */
+/* TODO: calibrate to useful value */
+#define MIN                 (100U)
+/* TODO: calibrate to useful value */
+#define SHIFT               (12U)
+#define FACTOR              DIV_ROUND(233UL << SHIFT, 100)
 
 int mq3_init(mq3_t *dev, adc_t adc_line)
 {
@@ -30,14 +34,15 @@ int mq3_init(mq3_t *dev, adc_t adc_line)
     return adc_init(dev->adc_line);
 }
 
-int mq3_read_raw(const mq3_t *dev)
+int16_t mq3_read_raw(const mq3_t *dev)
 {
     return adc_sample(dev->adc_line, PRECISION);
 }
 
-int mq3_read(const mq3_t *dev)
+int16_t mq3_read(const mq3_t *dev)
 {
-    float res = mq3_read_raw(dev);
+    uint32_t res = mq3_read_raw(dev);
     res = (res > MIN) ? res - MIN : 0;
-    return (int)(res * FACTOR);
+    /* same as `(int16_t)(res * 2.33)` */
+    return (res * FACTOR) >> SHIFT;
 }
diff --git a/tests/pkg/lvgl/main.c b/tests/pkg/lvgl/main.c
index d1c8130fdf..9bff368b1f 100644
--- a/tests/pkg/lvgl/main.c
+++ b/tests/pkg/lvgl/main.c
@@ -92,7 +92,7 @@ void sysmon_create(void)
 
     /* Create a chart with two data lines */
     chart = lv_chart_create(cont);
-    lv_obj_set_size(chart, hres / 2.5, vres / 2);
+    lv_obj_set_size(chart, hres * 10L / 25, vres / 2);
     lv_obj_set_pos(chart, LV_DPI_DEF / 10, LV_DPI_DEF / 10);
     lv_chart_set_point_count(chart, CHART_POINT_NUM);
     lv_chart_set_range(chart, LV_CHART_AXIS_PRIMARY_Y, 0, 100);
@@ -102,7 +102,7 @@ void sysmon_create(void)
 
     /* Set the data series to zero */
     uint16_t i;
-    for(i = 0; i < CHART_POINT_NUM; i++) {
+    for (i = 0; i < CHART_POINT_NUM; i++) {
         lv_chart_set_next_value(chart, cpu_ser, 0);
         lv_chart_set_next_value(chart, mem_ser, 0);
     }