One metre of extension per metre of original length — strain expressed as a plain ratio. Because it is a length divided by a length the units cancel, which is why a strain can be quoted in metres per metre, inches per inch or microstrain and mean exactly the same thing.
Watch out: Engineering strain and true strain are different quantities sharing this unit. Engineering strain divides by the ORIGINAL length and true strain integrates over the changing one, so they agree at small values and diverge once deformation is large. A tensile curve past necking plotted as engineering strain is not the material's real behaviour.
| 1 (Strain) | 1 |
| 1 (Slope) | 1 |
Strain earns its own unit family despite being dimensionless because the numbers involved are so small that a bare ratio is unreadable. Structural steel yields near 0.002, and most working strains sit between 0.0001 and 0.003 — which is why the trade almost never writes the ratio itself and reaches instead for microstrain, where those become 100 and 3000.
One metre of rise per metre of run: a slope, grade or hydraulic gradient as a plain ratio. It is dimensionless because it is a length over a length, and it is the form every slope formula computes in.
One meter per meter in every strain unit
| 1 | meter per meter (m/m)this unit | |
| 1 | inch per inch (in/in) | |
| 1,000,000 | microstrain (µm/m) | |
| 1,000 | millimeter per meter (mm/m) | |
| 1,000 | mil per inch (mil/in) | |
| 100 | percent strain (%) |
One meter per meter in every slope unit
| 1 | meter per meter (m/m)this unit | |
| 100 | percent grade (%) | |
| 1,000 | millimeter per meter (mm/m) | |
| 1,000 | per mille (‰) | |
| 1 | foot per foot (ft/ft) | |
| 12 | inch per foot (in/ft) |