ratio for concret mix

[jor96alb37da]

what is the ratio for a concret mix for foundations

[Clanad]

3 sand, 4 gravel and 1 cement mix...

[Ankou]

it really depends what for, scroll down to Table 3.12 for grade, mix ratios and general uses.....

http://www.fao.org/docrep/S1250E/S1250E08.htm

generally you are probably looking at a C20 (1:2:4) mix for most uses, which is 1 x cement + 2 x Grit Sand + 4 x gravel.

[gordyagusta]

1st and foremost , The table refered to is largely irrelevant because of changes in the regulations by the QSRMC, both previous answers are correct to some degree, but you need to provide more information regarding what you intend to build on top of the foundation ie, garden wall, garage, single storey extention, 2 storey extention? Also you need to take into consideration the soil type you are digging into ie acidic/alkaline properties.
In my opinion you should be aiming for at least a C30Nm strength concrete but ideally and without doubt I would always recommend C35Nm concrete for foundations. To substantiate my opinion I have been in the concrete supply industry for over 15yrs... Tell me more about the foundations I can give you a more specific mix, even tell you how much material you require... and an expected cost...