function suma(){
        var sum1 = document.getElementById("sum1");
        var sum2 = document.getElementById("sum2");
        var input = document.getElementById("results");
        results = (sum1.value * sum2.value);
        input.value= results;
    }
    function percentage(){
        var results = document.getElementById("results");
        var input = document.getElementById("premium");
        var premium1 = 0.01*results.value;
        document.getElementById("premium").value=premium1;
    }

<div class="col-sm-4 form-group">
    <label class="text-primary"><strong><?php echo $PesoKg; ?>&nbsp;(<?php
    echo $_SESSION['ge_measure']; ?>)<strong></label>
    <input type="number" class="form-control" required onblur="if(this.value
    == ''){this.value='0'}" onKeyUp="suma();"  id="sum2"   name="Weight"
    value="0" />
    </div>
    <div class="col-sm-4 form-group">
    <label class="text-primary"><strong>Amt&nbsp;<?php echo $PrimerKilo; ?
    >&nbsp;<?php echo $_SESSION['ge_measure']; ?><strong></label>
    <input type="text" class="form-control" onblur="if(this.value == '')
    {this.value='0'}"  onKeyUp="suma();" id="sum1"    name="variable"
    value="3.25" />
    </div>
    <div class="col-sm-4 form-group">
    <label class="text-primary"><strong><?php echo $SubtotalEnvio; ?><strong>
    </i></label>
    <input  type="text" class="form-control" name="shipping_subtotal"
    id="results" value="0" />
    </div>

    </div>
    <div class="col-sm-6 form-group">
    <label class="text-primary"><strong>Insurance 1%<strong></label>
    <input type="number" class="form-control"  id="insurance"
    name="insurance" required onblur="if(this.value == ''){this.value='0'}"
    onKeyUp= "percentage();" name="variable" value="0.01" >
    </div>
    <div class="col-sm-6 form-group">
    <label class="text-primary"><strong>Premium<strong></label>
    <input type="number" class="form-control"  id="premium" name="premium"
    value="0" >
    </div>