this article says that for 1978, A14 dish was either 4mm or 5mm.

Sorry DD,
It was a separate question. I know I'll need to measure the dish plus the combustion chamber. I'm building a new A14 and I'm aiming for 10:1 compression. Wondering if I can get there with these pistons as opposed to having forged ones made.Although, I was also hoping to go for a 78mm bore...

As I recall both 1mm dish and 2mm dish are common in USA for A14. Perhaps one was used in the FU Engine and the other is the 'regular' piston. There are at least three different combustion chamber designs in USA (two are unique to USA, the FU Head and the 1981/1982 head)

My pistons have that stupid little key hole that indicates the front of the piston, I'm not a facebook fan of that. I am a fan of the 1 mm dish in them :)

The formula won't help you. What you need to know is:
1. What is the dish on typical/common A14
2. What is the dish you have?

You can easily get #2. Others here can report #1.
To measure the dish, cut a 1/8 plexiglass to fit over the piston, and drill a small hold towards one side. Then use syringe from a feed store, and see how many CCs it takes to fill the dish.

The dish seems shallow to me... What is the formula for calculating compression ratio?

Those look identical to the ones I have at home except mine are 76mm and are easily available here in Zimbabwe.They are A14 pistons that's for sure.

Mine are after market DD,i'm not suggesting there genuine Nissan.
You will notice the dish is heaps less than the standard dish
Can't remember the "cc" differance but it's substantial.
Very desirable,so look after them.

I will guess they are NOT stock. Stock pistons are not .050 overbore, nor are factory overbore pistons marked 050. Instead they will be 0.5, 1.0 or 1.5 mm overbore.

But they look to have a factory-style dish. I have seen deeper ones, and ones that have an offset dish.

There the higher comp A14 pistons and the obvious oversize markings.
There getting quite hard to find in Oz but i have one new set
for my next rebuild sitting on the shelf.