For either powder suspensions or colloidal solid-liquid dispersions ─ hereafter also taken as suspensions ─ mass ratio concentrations (i.e. mass of solid : mass of suspension) or the corresponding percent ratios are widely used. They are independent of the temperature and readily unambiguously defined, what does not occur with either mass/volume ratios or volume/volume ratios. Furthermore, mass/volume ratios depend on the unit system used. One often face the problem of finding the volume (or  mass) of dispersant needed to obtain a suspension of a given mass ratio, by mixing a known mass of powder with that volume of dispersant. To address this problem, being mass ratio concentrations used; let us call the mass of solid powder, Mp, the mass of dispersant Md, and the mass of suspension Ms. The mass balance for the mixing operation reads: Mp + Md = Ms. The mass ratio of the suspension is given by: R = Mp / Ms. The mass of dispersant can now be obtained from last equations, being conveniently given as: Md = [(1/R) - 1]·Mp. To obtain the corresponding volume of dispersant, one would obviously need to know its density for the temperature considered.  

For the volume of dispersant needed to dilute a suspension, you may check: https://www.researchgate.net/post/How_can_I_reduce_the_concentration_of_silica_suspension

Another problem often found dealing with suspensions is that of finding the mass of solid powder (Mp) needed to obtain a known volume of suspension (Vs) of a given mass ratio (R= Mp / Ms). Considering mass balance for the mixing operation (Mp + Md = Ms), where Md stands for mass of dispersant, it follows that Mp = Md / [(1/R) - 1].(*) Let the volume of the solid powder, of suspension, and of dispersant, be denoted as Vp, Vs, Vd; and the corresponding densities as ρP, ρs, ρd. Accepting volume additivity (i.e. volume balance holds) we may write Vd = Vs - Vp, and since Md = Vd·ρd and Vp = Mp/ρP, we have Md = (Vs - Mp/ρP)·ρd. Substitution of last equation at (*) yields, after some transformation Mp = Vs·[ρd / (1 - R·(1 - ρd/ρP))]·R, solving this problem.  

Still another problem of practical interest that may be found dealing with suspensions is to estimate suspension’s density for a given concentration. Partial substitution of concentration given as mass ratio R = Mp / Ms at the final equation taken from last answer, here slightly rewritten as Mp/Vs = [ρd /(1 - R·(1 - ρd/ρP))]·R, conducts to the wanted estimate of the density of the suspension (ρs = Ms /Vs) as a function of the mass ratio concentration: ρs = ρd /(1 - R·(1 - ρd/ρP)).

Once we have considered the problem examined at last answer, we may pose ourselves the inverse question, meaning, that of estimate the mass ratio concentration of a suspension (R) after measuring its density, ρs. To solve this problem we just have to transform the equation obtained with last answer, to express R as function of the measured density: ρs = ρd /(1 - R·(1 - ρd/ρP)). For the sake of simplicity, it is now convenient to define (dimensionless) relative densities for the suspension and the solid powder, taken with regards to the dispersant; ρs*= ρs/ρd and ρP*= ρP/ρd. After some transformation, we are lead to the wanted equation, R = (1 - 1/ρs*) / (1 - 1/ρP*).

BRONGNIART’S FORMULA ─ Let G stand for the relative density of the solid powder with regards to water (dispersant) at the temperature of slip (ceramic suspension): G = ρP*= ρP/ρw, being ρP and ρw densities of powder and water (g/ml). Let L´ be the mass (g) of 1 litre of slip and W´ be the mass of powder (g) in 1 litre of slip, so that is given by W´ = R·L´. We recall that R is the mass ratio concentration (R = Mp / Ms). By W and L we denote the numerical values of previously defined quantities (W = W´/g; L = L´/g). The relative density of the slip is ρs*= ρs/ρw, being its density ρs = Ms /Vs = L·g/(1000 ml). We may now write L = ρs·1000 ml/g = 1000·ρs*, where it was accepted that ρw ≈ 1 g/ml. We also have W = R·L. After substitution of R as obtained in previous answer, we have W = G·(L - L/ρs*) / (G - 1), i.e. W = G·(L - 1000) / (G - 1). This is the well-known Brongniart’s formula [*], widely used by practical ceramists and potters. 

[*] First published in “Traité des Arts Céramiques ou des Poteries”, Vol. 1, 1854, p. 249; http://members.optusnet.com.au/rogergraham/brongniarts_formula_made_easy.pdf

COAL SLURRY DENSITY FORMULA ─ Still concerning to the problem of finding suspension’s density for known concentration, we recall that we have found at a previous answer that ρs = ρd / (1 - R·(1 - ρd/ρP)). For water as the dispersant, ρd ≡ ρw ≈ 1 g/ml, while relative density of suspension and powder is ρs*= ρs/ρw and ρP*= ρP/ρw. We further recall that R is the mass ratio concentration, R = Mp / Ms. Let us call R* to this same ratio, but given as percentage and with the % symbol omitted, i.e. R* = 100·R. The above mentioned formula now rewrites as ρs* = 100 / (100 – R* + R*/ρP*). With this form appears published by R. Symington [*], which calls R* (in the quoted reference actually denoted by C) the «weight concentration of the solids in suspension», to which “gm/cc” units are erroneously ascribed, even considering that the author seemingly wanted to refer to the numerical value of the quantity expressed with such units ─ otherwise last equation would be dimensionally incorrect. This point is mentioned because it reflects the messy units and symbol definitions often met when considering some of the versions of similar formulas published in literature.

[*] R. Symington, “Dense medium coal washing”, Chap. 11, in: H.W. Cremer, T. Davies (Eds.), “Chemical Engineering Practice”, Vol. 3: “Solid Systems”, Butterworths Scientific Publications, London, 1957, p. 313.   

The simplest way of calculating solid volume fraction dispersed in a carrier or solvent is by measuring a density of carrier and fluid, whether it is concentrated or diluted. You can find the formula to solid volume fraction from densities in many research papers. You can find my research paper also.