Resuspension Calculator

Frequently asked questions

What is a resuspension calculator used for?

A resuspension calculator converts a known amount of pelleted or dried material into a concentration. Give it the total cell count (or OD600 reading, hemocytometer count, or bead mass) and the buffer volume, and it returns cells per mL, mg per mL, or particles per mL — plus the reverse calculation: what volume you need to hit a target concentration.

How do I calculate concentration after resuspending a cell pellet?

Divide the total number of cells in the pellet by the resuspension volume in milliliters: concentration (cells/mL) = total cells ÷ volume (mL). For example, resuspending 2 × 10⁹ cells in 5 mL of buffer gives 2 × 10⁹ ÷ 5 = 4 × 10⁸ cells/mL.

How much buffer do I need for a target cell concentration?

Rearrange the same formula: required volume (mL) = total cells ÷ target concentration (cells/mL). For example, to resuspend 5 × 10⁷ cells at a target of 1 × 10⁶ cells/mL you need 5 × 10⁷ ÷ 1 × 10⁶ = 50 mL of buffer.

How do I convert OD600 to cells per mL?

Multiply the OD600 reading by the organism's conversion factor: cells/mL = OD600 × factor. For E. coli use 8 × 10⁸ cells/mL per OD unit, so OD600 = 0.6 gives 0.6 × 8 × 10⁸ = 4.8 × 10⁸ cells/mL. For baker's yeast use 3 × 10⁷, so OD600 = 1.2 gives 1.2 × 3 × 10⁷ = 3.6 × 10⁷ cells/mL. Factors are strain- and instrument-dependent, so calibrate against plate counts for critical work.

How do I calculate cell concentration from a hemocytometer count?

Count the cells in the 4 large corner squares, average them, multiply by the dilution factor, then multiply by 10⁴: cells/mL = average count × dilution × 10⁴. Example: counts of 120, 118, 125, 117 (average 120) with a 2-fold trypan blue dilution give 120 × 2 × 10⁴ = 2.4 × 10⁶ cells/mL.

How do I calculate particles per mL from a bead mass?

Treat each bead as a sphere: volume = π/6 × diameter³, mass per bead = density × volume, total beads = mass ÷ mass per bead, then divide by the resuspension volume. Example: 1 µm polystyrene beads (density 1.05 g/cm³), 10 mg resuspended in 2 mL, give about 9.09 × 10⁹ particles/mL.

How do I make a target cell suspension from a concentrated stock?

Use the dilution equation: stock volume = target concentration × final volume ÷ stock concentration. Example: from a 5 × 10⁷ cells/mL stock, to make 10 mL at 2 × 10⁶ cells/mL, take 2 × 10⁶ × 10 ÷ 5 × 10⁷ = 0.4 mL of stock and add buffer to 10 mL.

How do I plan a serial dilution for plating?

Pick a dilution factor (usually 10-fold), the number of steps, and the plated volume; each step's concentration is stock ÷ factor^step and colonies per plate = concentration × plated volume. Example: from 4 × 10⁸ cells/mL with 10-fold steps and 0.1 mL plated, step 3 gives 4 × 10⁵ cells/mL (40,000 CFU per plate) and step 6 gives 40 CFU per plate — inside the countable 30–300 colony window.

What is the difference between resuspension and reconstitution?

Resuspension means adding buffer to material you already have as a pellet or dry deposit — typically cells after centrifugation or beads after storage — to reach a target cell or particle concentration. Reconstitution means dissolving a manufactured dry powder (for example a lyophilized antibiotic or drug in a vial) in a diluent to reach a labeled concentration.

Working from a dry vial instead? Use our Reconstitution Calculator.

How accurate are resuspension calculations?

These are planning estimates, not measurements. OD600 factors vary by strain, growth phase, and spectrophotometer; hemocytometer counts carry sampling error; bead diameters have size distributions. Always verify critical concentrations empirically — for example by plate counts or a recount — before experiments that depend on them.

What buffer should I use to resuspend a cell pellet?

Use a buffer that keeps your material viable and compatible with the next step: PBS or sterile saline for washed bacterial pellets, complete growth medium or PBS for mammalian cells, and the manufacturer's recommended storage buffer for beads. Match pH and osmolarity to the cells, and avoid buffers that interfere with downstream assays.

What if the calculated resuspension volume is too small to pipette?

If the calculated volume is below what you can pipette accurately (roughly 1–2 µL for most micropipettes), resuspend in a larger, practical volume first, then dilute to the target — or concentrate more starting material. The calculator's target-volume mode shows the exact number; use the serial dilution helper to plan the extra step.