Svg icon inconsitency

I want to use svg icons with dimensions 24x24. But when i make all of them to the same dimension some of them become large and some small. I was not using frame under the icon. Like should i use frame under the icon and will that help? And what is the difference in placing the icon in a frame of 24x24 and manually adjusting its dimension to 24x24, are they not the same thing and will produce the same output?