We've done lots of testing in house and know that adequate space between the design and the edge of the stencil is super helpful to keeping paint off the background surface so we always include a nice margin for error! We do our best to include at least one inch of vinyl around each side of the design for a stencil. If that not possible (for some of our larger designs) you can easily add more mask with painter's tape or masking tape to prevent over painting. This extra space is plenty for hand-painting, but if you want to use a spray paint, just use paper, painter's tape, blasting sheeting (anything you want, really) to cover a larger surface and protect your project from overspray.
Example: If a design is noted as 5 inch by 17.5 inch, you will receive the stencil with an outer dimension of 7 inch by 19.5 inch, but the design will remain the listed size..