Geometry
Perimeter rearranged for a missing side
Divide the perimeter by two to get the half sum, then subtract the side you already know.
The Formula
w = P / 2 - l
Divide the perimeter by two to get the half sum, then subtract the side you already know.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| w | Width | metres | The side being solved for. |
| P | Perimeter | metres | Known total distance around. |
| l | Length | metres | The known side. |
What Each Symbol Means
wmetres
Width
The side being solved for.
Pmetres
Perimeter
Known total distance around.
lmetres
Length
The known side.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate the perimeter of a rectangle page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate The Perimeter Of A Rectangle, filed under Math. Every number the guide produces comes from substituting into this one line.