# Read / Write Capacity Units
This is for [[_DynamoDB|DynamoDB]].

## Writing
Math goes sort of like this:
$$
\begin{aligned}
w &= \text{write} \\
tw &= \text{transactional write} \\
\ \\
1\ WCU &= 1\ kb/w/s \\
2\ WCU &= 1\ kb/tw/s \\
\end{aligned}
$$
Take away is that a 1KB write is 1WCU. And a 1KB [transactional]{.underline} write is 2WCU.
## Reading
The math for reading is a little bit more convoluted, because the reads are divided by 4KB blocks.
$$
\begin{aligned}
cr &= \text{consistent read} \\
ecr &= \text{eventually consistent read} \\
tr &= \text{transactional read} \\
\ \\
1\ RCU &= 4kb/cr/s \\
\frac{1}{2}\ RCU &= 4kb/ecr/s \\
2 RCU &= 4kb/tr/s
\end{aligned}
$$