Hi! How old are your guinea pigs? I am sorry, but your measurements sound a bit out - adult guinea pigs are around one kilo (kg).
Guinea pig weights can vary massively right from when they are born and that also holds for adult guinea pigs.
What you look out for in younger guinea pigs up to 4-6 months old is that they put on weight every week. After that, the weight gain is slowing down. Guinea pigs stop growing around 12-15 months old, but if you overfeed, they will grow sideways.
Because the individual weight can vary so massively, you also check for the "heft", the size/weight ratio. You do this around the ribcage - you should just about feel the single ribs, but they should neither be buried (overweight) or stand out noticeably (underweight).
Monitoring the weight is a health control measure. What you are looking out for is less weight gain and more weight loss - the latter is if it is more than 50g/2 oz should be seen by a vet, if it is more then 100g/3 oz promptly and if the weight loss has happened within 24 hours ASAP as an absolute life and death emergency. Whenever you are worried about the health, you switch to weighing daily at the same time.
Please take the time to read through this guide here. It explains what are normal weight ranges, how you feel the heft, and how you control the weight.
The Importance Of Weighing - Ideal Weight / Overweight / Underweight