Answers for "input small bootstrap"

large input box bootstrap 4

.form-control-sm
.form-control-lg

boostrap input tag

<input class="form-control form-control-lg" type="text" placeholder=".form-control-lg">
<input class="form-control" type="text" placeholder="Default input">
<input class="form-control form-control-sm" type="text" placeholder=".form-control-sm">