What is the wafer price for the 28-nanometer wafer that is needed to achieve a similar return on investment for the P6 28-nanometer foundry capacity
- you already had to consider the possible overbooking?
Jason Wang -- Director and President
Absolutely. I mean, this is a planning 101. So we have to consider that. And we actually -- based on our research and study, we're actually going back all the way to the end market, entire pipeline in terms of the supply chain to analysis that. So I think that there's a few mega trends in this space driving the demand, from 5G smartphones, the automotive, EV adoption, as well as the learn-from-home, work-from-home space. And so those demands are real, OK?
So -- and if you look at the past years, there's lack of capex in the mature node space. So structurally, they're just not enough. And so that's why we believe, even with the P6 or even with any announced capacity today in the foundry space, we still believe this -- the structural shortage will probably remain.
Stephen Chan -- Asia Capital -- Analyst
Yes. Thank you. Very clear and very good results. Thank you.
Jason Wang -- Director and President
Thank you, again.
Operator
Ladies and gentlemen, we are running out of time. So we're taking the last question. And the last one is from Bruce Lu Goldman Sachs, go ahead please.
Bruce Lu -- Goldman Sachs -- Analyst
Okay. Thank you for taking my question again. I have a question about ASP. For the first quarter, ASP as a blended base improved by 1.3% only and -- which is pretty much driven by like more 28-nanometer product mix improvement. So where is the price hike that market is talking about? I mean also for the second quarter, the capacity is growing by 4%, but shipment is growing by 3%. But I'm assuming that the new capacity addition is mainly for 28-nanometer capacity, which is supposed to have a much bigger or much higher ASP. The ASP guidance for second quarter is also like 3%, 4% only, which is, again, pretty much driven by 28. So as a like-to-like base ASP, do we see any improvement?
Chi-Tung Liu -- Chief Financial Officer
Well, there's [Indecipherable] to correct. The first quarter ASP growth was actually more than 3%, not one point something. So as I mentioned about -- some of that comes from price increase, so less than 3.2%. And some of that comes from product mix improvement. So overall, quarter one ASP growth was more than 3%.
Bruce Lu -- Goldman Sachs -- Analyst
I see. What is the forex assumption in first quarter? Because it's using like...
Jason Wang -- Director and President
Forex was 28.3, so there was nearly 2% negative impact on forex.
Bruce Lu -- Goldman Sachs -- Analyst
I see. Understand that. Understand that. So for the second quarter, what is the ASP -- what is the assumption for the ASP expansion driven by the product mix improvement?
Jason Wang -- Director and President
Still similar. I would say both are key factors, which contribute nearly 50-50 each. So we normally don't give the detailed numbers, but you should expect to see a similar driving force for this 4% growth for quarter two in ASP.
Bruce Lu -- Goldman Sachs -- Analyst
I see. Okay. Last question, I just did a very quick math for the P6 28-nanometer wafer price. It seems to me that you want to have a similar return. The wafer price for that 28 has to be like 50%-plus higher than the current market price. That seems too good to be true from my simple math. So, is there anything I'm missing or is that math sounds correct?
Chi-Tung Liu -- Chief Financial Officer
I can't really comment on percentage, but there is a predetermined pricing arrangement with the customers. It's actually a very diversified customer portfolio. So it -- well, I mean the bottom line is the mechanism works. I mean the math work, OK?
Bruce Lu -- Goldman Sachs -- Analyst
The math -- so my math work?
Chi-Tung Liu -- Chief Financial Officer
So it's -- yes, I can't comment about the percentage of that.
Jason Wang -- Director and President
Basically wrong in one effect of the total ROI calculation. We also factor in the benefit of the economy of scale and also the cost reduction effort and etc, etc. The -- all the factors Chi-Tung just mentioned. So again, it's a collective factor.
Br
- you already had to consider the possible overbooking?
Jason Wang -- Director and President
Absolutely. I mean, this is a planning 101. So we have to consider that. And we actually -- based on our research and study, we're actually going back all the way to the end market, entire pipeline in terms of the supply chain to analysis that. So I think that there's a few mega trends in this space driving the demand, from 5G smartphones, the automotive, EV adoption, as well as the learn-from-home, work-from-home space. And so those demands are real, OK?
So -- and if you look at the past years, there's lack of capex in the mature node space. So structurally, they're just not enough. And so that's why we believe, even with the P6 or even with any announced capacity today in the foundry space, we still believe this -- the structural shortage will probably remain.
Stephen Chan -- Asia Capital -- Analyst
Yes. Thank you. Very clear and very good results. Thank you.
Jason Wang -- Director and President
Thank you, again.
Operator
Ladies and gentlemen, we are running out of time. So we're taking the last question. And the last one is from Bruce Lu Goldman Sachs, go ahead please.
Bruce Lu -- Goldman Sachs -- Analyst
Okay. Thank you for taking my question again. I have a question about ASP. For the first quarter, ASP as a blended base improved by 1.3% only and -- which is pretty much driven by like more 28-nanometer product mix improvement. So where is the price hike that market is talking about? I mean also for the second quarter, the capacity is growing by 4%, but shipment is growing by 3%. But I'm assuming that the new capacity addition is mainly for 28-nanometer capacity, which is supposed to have a much bigger or much higher ASP. The ASP guidance for second quarter is also like 3%, 4% only, which is, again, pretty much driven by 28. So as a like-to-like base ASP, do we see any improvement?
Chi-Tung Liu -- Chief Financial Officer
 Well, there's [Indecipherable] to correct. The first quarter ASP growth was actually more than 3%, not one point something. So as I mentioned about -- some of that comes from price increase, so less than 3.2%. And some of that comes from product mix improvement. So overall, quarter one ASP growth was more than 3%.
Bruce Lu -- Goldman Sachs -- Analyst
I see. What is the forex assumption in first quarter? Because it's using like...
Jason Wang -- Director and President
Forex was 28.3, so there was nearly 2% negative impact on forex.
Bruce Lu -- Goldman Sachs -- Analyst
I see. Understand that. Understand that. So for the second quarter, what is the ASP -- what is the assumption for the ASP expansion driven by the product mix improvement?
Jason Wang -- Director and President
Still similar. I would say both are key factors, which contribute nearly 50-50 each. So we normally don't give the detailed numbers, but you should expect to see a similar driving force for this 4% growth for quarter two in ASP.
Bruce Lu -- Goldman Sachs -- Analyst
I see. Okay. Last question, I just did a very quick math for the P6 28-nanometer wafer price. It seems to me that you want to have a similar return. The wafer price for that 28 has to be like 50%-plus higher than the current market price. That seems too good to be true from my simple math. So, is there anything I'm missing or is that math sounds correct?
Chi-Tung Liu -- Chief Financial Officer
I can't really comment on percentage, but there is a predetermined pricing arrangement with the customers. It's actually a very diversified customer portfolio. So it -- well, I mean the bottom line is the mechanism works. I mean the math work, OK?
Bruce Lu -- Goldman Sachs -- Analyst
The math -- so my math work?
Chi-Tung Liu -- Chief Financial Officer
So it's -- yes, I can't comment about the percentage of that.
Jason Wang -- Director and President
Basically wrong in one effect of the total ROI calculation. We also factor in the benefit of the economy of scale and also the cost reduction effort and etc, etc. The -- all the factors Chi-Tung just mentioned. So again, it's a collective factor.
Br