Make one variable double the value of the other with SASS

Make one variable double the value of the other with SASS

Im using SASS. I need on value to be double another value so the logic is
this:
.one {
padding: 'value';
}
.two {
padding: 'value times 2';
}
So it could be this:
.one {
padding: 2px;
}
.two {
padding: 4px;
}
Or this:
.one {
padding: 10px;
}
.two {
padding: 20px;
}
How can I write this?