To calculate the effective memory clock, you will need your memory type and normal memory clock. The memory clock is multiplied by either 2, 4, 8 or 16 depending on which memory type you have. This is due to the fact that some memory types can send data multiple times per clock cycle. For instance, GDDR5 memory is quad pumped which means it can send data 4 times per clock cycle. So any graphics card with GDDR5 memory would have an effective memory clock of 4 times the default memory clock.
The equation is: Effective Memory Clock = Memory clock x how many times that memory type can send per clock cycle
To view how many times each memory type can send per clock cycle, refer to the table below.
If you’re looking for the other way around (effective memory clock to normal memory clock) then click here.
Example Calculation
The Nvidia GeForce RTX 3060 has a memory clock of 1875 MHz and has GDDR6 memory. GDDR6 memory is 8 pumped, and so can send data 8 times per clock cycle. Therefore, the effective memory clock = 1875 * 8 = 15000 MHz. This is the same as 15000 Mbps or 15 Gbps.
Why is the effective memory clock higher
The effective memory clock is usually bigger than the normal memory clock because of the fact that modern day memory can send data multiple times per cycle. The default memory clock is the actual speed of the memory chips but this doesn’t take into account how many times data can be sent per clock cycle.
In 1998 DDR ram short for double data rate was released and allowed data to be sent two times per clock cycle (hence the double name). It sent data on both the rising and falling edge of the clock cycle. This technology was and is still used on lots of types of ram including DDR3. GDDR5 ram allowed there to be 4 data transfers per clock cycle, thus increasing the effective memory clock. GDDR5x and GDDR6 allowed for 8 data transfers per clock cycle. And finally, GDDR6x allowed for 16 data transfers per clock cycle.
How many time data can be sent per clock cycle table
| Memory Type | How many times data can be sent per clock cycle |
|---|---|
| GDDR6X | 16 |
| GDDR6/GDDR5x | 8 |
| GDDR5/LPDDR5 | 4 |
| SDR (or other single data rate memory types) | 1 |
| Everything Else including DDR,DDR2,DDR3,DDR4,HBM,HBM2,HBM3 etc | 2 |
