Sandpaper coarseness is indicated by numbered grits. As the grit numbers get smaller, the sandpaper gets coarser.
Coarse sandpaper makes deep scratches. Those deep scratches need to be removed completely by “stepping-up” with gradually finer grits before painting. If not, you will see sand scratches in your finished paint job.
How big of a step between grits is too big?
While making smaller steps is fine, consider the following guidelines for the biggest steps:
- For P24-P320, choose a grit that is 2 times your current grit number.
- For P400 and finer, step-up 1.5 times your current grit number.
This rule of thumb only works if you stick to sandpapers in the same rating scale.
Sandpaper Rating Scales Explained
There are two scales commonly used to rate sandpaper coarseness:
- P-scale, sometimes called the European or FEPA scale
- ANSI scale, sometimes called the US Standard or CAMI scale
The differences between the two scales is minimal in the coarser grits. In finer grits, a P-scale sandpaper will be coarser compared to an ANSI sandpaper with the same grit number. When choosing sandpaper above P600 or its equivalent, it’s very important to know which scale it is. A mistake here could ruin your paint job.
The following chart shows how the scales compare, and the biggest step you can make between common grits. For example:
- P400 grit is equivalent to ANSI 320 grit. The maximum step you should make is to either P600 or ANSI 400.
| Uses | P-Scale Grit Number | Equivalent ANSI Scale Grit Number | Biggest Step for P-Scale/ANSI |
| heavy metal removal, grinding welds, rust removal | P24 | 24 | P40/40 |
| metal removal, weld finishing | P36 | 36 | P60/60 |
| medium metal removal, heavy paint removal, initial shaping of reinforced Body Filler | P40 | 40 | P80/80 |
| P60 | 60 | P120/120 | |
| initial shaping of body filler, paint removal, finishing metal before primer | P80 | 80 | P180/180 |
| P120 | 120 | P220/220 | |
| final straightening of body filler, sanding out chips and defects in old paint | P180 | 180 | P320/320 |
| P220 | 220 | P400/320 | |
| final sanding before primer or final straightening step when block sanding primer | |||
| P320 | None | P600/400 | |
| P400 | 320 | ||
| final sanding before paint | P600 | 400 | P1000/600 |
| P800 | 500 | P1200/600 | |
| heavy defect and texture removal in finished paint | P1000 | 600 | P1500/800 |
| P1200 | |||
| light defect and medium texture removal in finished paint | P1500 | 800 | P2000 or heavy duty rubbing compound |
| light texture removal in finished paint, removing P1500 scratches | P2000 | 1000 | rubbing compound |
| removing P2000 scratches | P2500 | 1500 | |
| P3000 |
Follow this link for a list of Recommended Grits for Automotive Paint Body Work