.input-xs {
    height: 22px;
    padding: 2px 5px;
    font-size: 12px;
    line-height: 1.5; //If Placeholder of the input is moved up, rem/modify this.
    border-radius: 3px;
}

.input-group-xs>.form-control,
.input-group-xs>.input-group-addon,
.input-group-xs>.input-group-btn>.btn {
    height: 22px;
    padding: 1px 5px;
    font-size: 12px;
    line-height: 1.5;
}

.input-group-sm>.form-control,
.input-group-sm>.input-group-addon,
.input-group-sm>.input-group-btn>.btn {
    height: 30px;
    padding: 5px 10px;
}