# EC / pH Calibration Standards — Temperature Compensation Chart
### 24.0°C – 26.0°C, 0.1°C increments

All standards are referenced to their nominal value at 25.0°C. Values below 25.0°C use the interpolated coefficient for that side of the curve; values above 25.0°C use the other side — buffers and conductivity standards are not perfectly linear in T, so a single global slope isn't used.

| T (°C) | EC 1413 µS/cm | EC 12880 µS/cm | pH 4.00 | pH 4.01 | pH 6.86 | pH 7.00 | pH 9.18 | pH 10.01 |
|:------:|:---:|:---:|:---:|:---:|:---:|:---:|:---:|:---:|
| 24.0 | 1385 | 12640 | 4.00 | 4.009 | 6.868 | 7.000 | 9.194 | 10.023 |
| 24.1 | 1388 | 12663 | 4.00 | 4.009 | 6.868 | 7.000 | 9.193 | 10.022 |
| 24.2 | 1391 | 12686 | 4.00 | 4.009 | 6.867 | 6.999 | 9.192 | 10.021 |
| 24.3 | 1394 | 12710 | 4.00 | 4.009 | 6.867 | 6.999 | 9.191 | 10.020 |
| 24.4 | 1396 | 12734 | 4.00 | 4.009 | 6.867 | 6.999 | 9.190 | 10.019 |
| 24.5 | 1399 | 12758 | 4.00 | 4.009 | 6.866 | 6.998 | 9.189 | 10.018 |
| 24.6 | 1402 | 12782 | 4.00 | 4.010 | 6.866 | 6.998 | 9.188 | 10.017 |
| 24.7 | 1405 | 12806 | 4.00 | 4.010 | 6.866 | 6.998 | 9.188 | 10.016 |
| 24.8 | 1407 | 12830 | 4.00 | 4.010 | 6.866 | 6.998 | 9.187 | 10.015 |
| 24.9 | 1410 | 12855 | 4.00 | 4.010 | 6.865 | 6.997 | 9.186 | 10.014 |
| **25.0** | **1413** | **12880** | **4.00** | **4.010** | **6.865** | **6.997** | **9.185** | **10.013** |
| 25.1 | 1416 | 12905 | 4.00 | 4.010 | 6.865 | 6.997 | 9.184 | 10.012 |
| 25.2 | 1419 | 12930 | 4.00 | 4.010 | 6.864 | 6.996 | 9.183 | 10.011 |
| 25.3 | 1421 | 12956 | 4.00 | 4.010 | 6.864 | 6.996 | 9.182 | 10.010 |
| 25.4 | 1424 | 12982 | 4.00 | 4.010 | 6.864 | 6.996 | 9.182 | 10.009 |
| 25.5 | 1427 | 13008 | 4.00 | 4.011 | 6.864 | 6.996 | 9.181 | 10.008 |
| 25.6 | 1429 | 13034 | 4.00 | 4.011 | 6.863 | 6.995 | 9.180 | 10.007 |
| 25.7 | 1432 | 13060 | 4.00 | 4.011 | 6.863 | 6.995 | 9.179 | 10.006 |
| 25.8 | 1435 | 13086 | 4.00 | 4.011 | 6.863 | 6.995 | 9.178 | 10.005 |
| 25.9 | 1437 | 13113 | 4.00 | 4.011 | 6.862 | 6.994 | 9.177 | 10.004 |
| 26.0 | 1440 | 13140 | 4.00 | 4.011 | 6.862 | 6.994 | 9.176 | 10.003 |

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### Sources & method

- **EC 1413 and 12880 µS/cm** — Hamilton Company published conductivity-vs-temperature reference tables (whole-°C resolution, KCl-based standards traceable to NIST/FDM). The 0.1°C values here are a local quadratic fit through each standard's 24, 25, and 26°C table points (captures the slight upward curvature visible in both series — e.g. 1413's slope is ~28 µS/cm/°C on the low side and ~27 on the high side, not perfectly linear).
- **pH 4.01, 6.86, 9.18, 7.00, 10.01** — Thermo Scientific Orion buffer-vs-temperature table (secondary NIST-traceable formulations), fit the same way using each buffer's 20, 25, and 30°C points. The 7.00 and 10.01 columns come from Orion's phosphate and borate/carbonate buffer series respectively — these are separate formulations from 6.86 and 9.18, not the same buffer relabeled.
- **pH 4.00** — Ricca Chemical's low-ionic-strength phthalate buffer, which is characteristically flat with temperature near this range (their table shows 4.00 at every 5°C step from 20–30°C); reported flat here rather than fabricating sub-hundredth movement the source doesn't show.

### Practical notes
- EC values are rounded to the nearest whole µS/cm — realistic given ±1% typical standard-solution tolerance.
- pH values are carried to 3 decimals to show the interpolated trend, but most benchtop meters display pH to 0.01 — treat anything below that as directional, not something your meter will actually resolve.
- If your bottles are a specific brand (Hanna, Oakton, Hamilton DuraCal, etc.), check the insert/COA — formulations for the "same" nominal pH differ enough between manufacturers (±0.01–0.02 pH, and sometimes different underlying buffer chemistry) that this chart is a solid general reference, not a substitute for the batch-specific certificate if you need last-digit accuracy.