A sketch can look well-proportioned when you make it because you can control the whole surface at once, but a wall is different. The arch, flower, wave, or lettering shape is too big for your hand and arm, which means you can’t control it as easily, and mistakes in placement are much easier to spot from across a room. Scaling allows your little sketch to become a big mural without getting squished against the top of the wall, the crown molding, and furniture, and without looking like a stretched blob.
Before you even think of making marks on the wall, place your little sketch up against a rough approximation of the area you intend to use for the mural. The approximation doesn’t have to look great. Figure out how tall and wide the area is going to be, and draw out a smaller rectangle with those proportions. If it’s a wide space, draw out a wide rectangle; for a smaller space, draw out a narrower rectangle. This helps you avoid trying to force a rectangle into a very long wall, or making the mural in an area that looks crowded and cramped.
One of the most common ways to scale up a design is to use a grid transfer. Lightly draw in a grid over your little sketch, then mark out a grid on your wall that will correspond to the one on your sketch. The marks for the wall need to be light. Use light pencil marks, a tape measure, and a level. Each of those grid squares on your sketch becomes a bigger one on your wall. You’ll be moving through the mural one small section at a time as you transfer your sketch. One of the grid squares will touch the corner of a curve you’re transferring. A leaf will touch another grid line. One of the border lines will run just beneath a grid line. These lines make the mural on a wall seem less overwhelming.
Keep your pencil marks very light. Hard pencil marks can show under the paint, especially if you use a pastel or light base coat color for the room. Press the pencil with enough pressure to draw lines you can see, but not so hard that every correction you make is going to stick around when you’re painting. If you are correcting a shape, stand a few feet away before you make a mark so you can tell if you’re actually off in your design, not just because you’re too close to see the shape as a whole.
Sometimes the hardest thing for artists to do is hold onto the positioning of the mural while getting up close to it for details. As you work, your body starts moving from side to side and an arc can end up going too high or low compared to the wall. When you’re marking your grid lines, or making small details, step back a few steps at a time to check the space from the bottom or the top of your design to the walls, ceiling, or molding. A level can help make a flat, horizontal line, but your eye, even from several feet away, will tell you whether your mural is centered or if a large, curved shape is out of place. This is especially true when transferring a wide shape like an arch, wave, big leaf, or a geometric pattern.
Do a quick scaling test before you start the real mural. Take any little shape, like a leaf, sun, mountain outline, or an abstract curved shape. Add a few grid lines to the shape and try scaling it up to a piece of cardboard, poster board, or a sheet of masking paper. Do it in pencil first, then make your final line with your detail brush. This will let you see how much further your hand has to reach when you enlarge a design. It will help you understand whether you can make some of the smaller curves and shapes in your mural with the brush you’re holding or if you have to adjust the design before transferring it to your wall.
Once you’ve transferred the big version of your sketch onto your wall, it can be tempting to jump right in with smaller details, but it’s not necessary. The transferred lines should only be a guide to help you know where to place painter’s tape, where to paint in your big blocks of color, and what your color palette will look like in the space. The transfer needs to be good enough that you can paint your big colors without being bound to the tiny little details and lines, but it needs to be a good enough guide that you don’t end up trying to figure out placement as you go. As long as it reads clearly on the wall before the paint touches it, scaling was a success.