How is the sample volume calculated?

Sample volume equals target mass divided by measured concentration. To load 20 µg from a 2 µg/µL lysate you pipette 10 µL. Lower-concentration samples need more volume, so the calculator also checks each fits in the well.

How much loading buffer do I add?

Loading buffer is added to reach 1× in the final volume. For a 4× buffer in a 20 µL well you add 5 µL (one quarter), since 4× diluted four-fold becomes 1×. The remaining volume after sample and buffer is made up with water.

What if a sample is too dilute to fit the well?

If the required lysate volume plus the loading buffer already exceeds the final well volume, you cannot reach the target mass at that well size. The calculator flags the sample so you can concentrate it, lower the target, or use a larger well.

Why normalise to equal protein per lane?

Western blot band intensity is only comparable across lanes if each carries the same total protein. Equal loading lets you attribute differences in band signal to the target protein's abundance rather than to how much lysate you happened to load.

Should I still run a loading control?

Yes. Even with careful normalisation, assays and transfers vary. A housekeeping loading control such as GAPDH, β-actin, or total-protein stain confirms equal loading and lets you correct the signal if needed.

What is the Western Blot Sample Preparation Calculator?

Enter measured protein concentrations for several lysates and a target protein mass per lane to get the sample volume, added water, and loading buffer for each well so every lane carries equal protein on an SDS-PAGE western blot. For molecular and cell biologists. It runs free in your browser on Gera Tools, with nothing uploaded.

Western Blot Sample Preparation Calculator

Name: Western Blot Sample Preparation Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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A western blot only quantifies protein abundance fairly if every lane carries the same total protein mass. This calculator takes each lysate’s measured concentration and works out exactly how much sample, water, and loading buffer to pipette so all lanes are normalised to one target mass in one final volume.

How it works

For each sample, the lysate volume needed is the target mass over the measured concentration, the loading buffer is a fixed fraction set by its strength, and water fills the rest:

sample_vol = target_mass / concentration
buffer_vol = final_vol / buffer_strength      (e.g. final/4 for 4× buffer)
water_vol  = final_vol − sample_vol − buffer_vol

If sample_vol + buffer_vol already exceeds the final well volume, the target mass cannot be reached at that well size and the sample is flagged.

Worked example

Suppose your target is 20 µg per lane in a 20 µL total well volume using 4× Laemmli buffer.

Sample	Concentration (µg/µL)	Lysate vol (µL)	Buffer (µL)	Water (µL)
A	2.5	8.0	5.0	7.0
B	1.0	20.0	5.0	— (over)
C	4.0	5.0	5.0	10.0

Sample B is too dilute at 1 µg/µL — 20 µg would require the entire well volume with no room for buffer. The calculator flags it so you know to concentrate the lysate (speed-vac, TCA precipitation, or ultrafiltration) or lower the target mass for the whole experiment.

Practical guidance

Choosing your target mass. For abundant cytoskeletal or housekeeping proteins, 10–20 µg is usually plenty. For low-abundance signalling proteins or phospho-isoforms, 30–50 µg may be needed. Setting your target based on the least-abundant sample you care about avoids the flagged-well problem.

Buffer strength matters. Most labs stock either 4× or 6× SDS sample buffer. A 4× buffer contributes one quarter of the final volume; a 6× contributes one sixth. Mixing up the denominator is a common error that either overdilutes the denaturing agents or leaves a well short — confirm the fold-concentration on your bottle before entering it.

Consistency across gels. If you run the same experiment on multiple gels or on different days, keep the target mass, final volume, and buffer identical. Even a small change propagates into your band-intensity comparisons.

Loading controls. Normalising to equal protein at the pipetting stage does not account for unequal transfer or gel running variation. Always run a housekeeping protein such as GAPDH or β-actin in the same blot, or use a total-protein stain (REVERT or Ponceau) on the membrane before blocking. These controls let you correct any residual lane-to-lane differences post-hoc.

Concentration method matters. BCA and Bradford assays differ in their sensitivity to detergents and reducing agents. If your lysis buffer contains SDS or high DTT, a compatible assay (BCA with a low-SDS tolerance, or an RIPA- compatible kit) will give more accurate concentrations and tighter normalisation.