علاوه بر متغییر آخری که داره تو سریال میاد بیرون باید متغییر us را هم float کنید
از این کد هم میتونید استفاده کنید:

کد:

// Demo sketch
// "is sketch will output distance info via the UART port
// port assignment
// change as may be necessary
const int trigger=6;
const int echo=7;
float distance;

void setup(){
Serial.begin(9600);
pinMode(trigger,OUTPUT);
pinMode(echo,INPUT);
}
void loop(){
// Trigger US-100 to start measurement
// Set up trigger
digitalWrite(trigger,LOW);
delayMicroseconds(5);
// Start Measurement
digitalWrite(trigger,HIGH);
delayMicroseconds(10);
digitalWrite(trigger,LOW);
// Acquire and convert to mtrs
distance=pulseIn(echo,HIGH);
distance=distance*0.01657;
// send result to UART
Serial.println(distance);
delay(50);
اینم یادم نیست تست کردم یا نه ولی فک کنم کار کنه :\

کد:
unsigned int EchoPin = 2;   // The Arduino's the Pin2 connection to US-100 Echo / RX
unsigned int TrigPin = 3;   // The Arduino's Pin3 connected to US-100 Trig / TX
unsigned long Time_Echo_us = 0; 
unsigned long Len_mm  = 0;  
void setup() { 
  
 //Initialize 
 Serial.begin(9600);         //  The measurement results through the serial output to the serial port on the PC monitor
 pinMode(EchoPin, INPUT);    //  The set EchoPin input mode.
 pinMode(TrigPin, OUTPUT);   //  The set TrigPin output mode.
}  

void loop() {   
  
  // By the Trig / Pin sending pulses trigger US-100 ranging
 digitalWrite(TrigPin, HIGH);                         // Send pulses begin by Trig / Pin
 delayMicroseconds(50);                               // Set the pulse width of 50us (> 10us)
 digitalWrite(TrigPin, LOW);                          // The end of the pulse    
 Time_Echo_us = pulseIn(EchoPin, HIGH);               // A pulse width calculating US-100 returned
 if((Time_Echo_us < 60000) && (Time_Echo_us > 1)) {   // Pulse effective range (1, 60000).
  // Len_mm = (Time_Echo_us * 0.34mm/us) / 2 (mm) 
  Len_mm = (Time_Echo_us*34/100)/2;                   // Calculating the distance by a pulse width.   
  Serial.print(Len_mm, DEC);                          // Output to the serial port monitor   
  Serial.println("mm");                               // Output to the serial port monitor
 }  
 delay(100);                                         // Per second (100ms) measured
}