ELISA Result Calculator

How to use this calculator

1. Enter blank ODs to correct background signal.
2. Enter standard concentrations with replicate ODs (up to three).
3. Select a curve type that matches your assay validation.
4. Add samples, their replicate ODs, and dilution factors.
5. Press Submit to calculate concentrations and QC flags.
6. Use CSV/PDF buttons to export your calculated table.

Formula used

• Blank mean = average(blank ODs).
• Mean OD = average(replicates).
• Blank-corrected OD = Mean OD − Blank mean.
• SD = sample standard deviation of replicates.
• CV% = (SD ÷ |Mean OD|) × 100.
• Linear: OD = m·Conc + b ⇒ Conc = (OD − b)/m.
• Log-linear: OD = m·log10(Conc) + b ⇒ Conc = 10^((OD − b)/m).
• 4PL: OD = d + (a−d)/(1+(Conc/c)^b), then inverted to solve Conc.
• Adjusted concentration = Conc × Dilution factor.

Example data table

These values are preloaded in the input tables for quick testing.

Choosing an Appropriate Standard Curve

This calculator supports linear, log-linear, and four‑parameter logistic fitting so the curve matches your assay behavior. For most sandwich ELISAs, 4PL captures the plateauing response at high concentration and the low-end asymptote near background. Use linear fitting when standards cover a narrow mid‑range and remain proportional. Use log-linear when responses are proportional to log10 concentration across several decades. To reduce bias, include at least six standards spanning the expected range and avoid extrapolation. A strong curve typically shows monotonic response and minimal residuals across concentrations for QC.

Blank Correction Improves Sensitivity

Background signal shifts every well upward, so blank correction is applied before fitting and interpolation. The blank mean is computed from your provided blank ODs and subtracted from each replicate mean. This improves low-end accuracy, tightens the standard curve near the detection limit, and reduces false positives. If blanks vary widely, repeat washing and confirm substrate timing to stabilize the baseline.

Replicate Statistics Strengthen Confidence

Each standard and sample can be entered with up to three replicates. The calculator reports mean OD, sample SD, and CV% so you can judge precision at a glance. As a practical rule, CV below 10% is strong, 10–15% is often acceptable, and values above 15% should trigger review. High CV commonly indicates pipetting variation, edge effects, or incomplete mixing.

Dilution Factors and Unit Reporting

The interpolated concentration is first calculated from the blank‑corrected OD, then multiplied by the dilution factor to return the original specimen concentration. For example, a 1:10 dilution uses a factor of 10. Keep units consistent with the standards (for example ng/mL or IU/mL) and report the same units in your worksheet and exports. If an OD falls outside the curve range, re‑run with an adjusted dilution.

Audit‑Ready Exports for Collaboration

After calculation, results can be exported as CSV for spreadsheets and as PDF for recordkeeping. The downloadable tables include replicate values, precision metrics, dilution factors, and final adjusted concentrations, supporting peer review and troubleshooting. Store exported files alongside plate maps and raw reader output for traceability. When sharing data, note the curve type and the blank mean used in the analysis.

FAQs

Which curve should I choose for most ELISA kits?

Use 4PL when the response plateaus at high concentration and approaches background at low concentration. Linear works for narrow mid‑ranges, while log-linear helps when the signal scales with log concentration.

Why do my samples show “Out of curve”?

This appears when blank-corrected sample OD is outside the fitted standard range. Recheck blanks, confirm standards, and rerun the sample with a higher or lower dilution to bring OD into range.

What CV% is acceptable for replicates?

Many labs target CV below 10% for strong precision. Values between 10–15% may be acceptable depending on SOP. Above 15% typically needs investigation, repeat pipetting, or re-reading.

How is dilution applied to the final concentration?

The calculator interpolates a raw concentration from the curve, then multiplies it by your dilution factor. For a 1:20 dilution, enter 20 to report the original specimen concentration.

Can I use two replicates instead of three?

Yes. Leave unused replicate fields blank; the mean and SD are computed from the available numeric values. More replicates generally improve precision estimates and help detect outliers.

Do the exports include all details needed for reporting?

The CSV and PDF include replicate ODs, mean, SD, CV%, dilution, and adjusted concentration. Save them with your plate map and raw reader file for complete traceability.