LESS Font and Line Height Mixin from: http://ajtroxell.com/less-font-and-line-height-mixin/

mixin.less

.font-size(@font-size: 16){
    @pxFontValue: (@font-size / 10);
    @pxLineValue: (@font-size / 10 * 1.5);
    font-size: @font-size * 1px;
    line-height: @font-size * 1.5 * 1px;
    font-size: ~"@{pxFontValue}rem";
    line-height: ~"@{pxLineValue}rem";
}

output.css

h1 {
    font-size:14px;
    line-height:21px;
    font-size:1.4rem;
    line-height:2.0999999999999996rem;
}

usage.less

h1 { .font-size(14); }