SPT N60 & (N1)60 Correction Calculator
Correct a field SPT blow count for hammer energy and overburden — the N60 and (N1)60 every correlation needs.
Raw N values from different rigs aren't comparable — an automatic hammer delivers ~30% more energy than a donut hammer on the same sand. Every modern correlation (liquefaction, φ, bearing) expects (N1)60, not field N.
Formula
Note: Educational aid — site characterization requires a geotechnical engineer.
SPT N60 & (N1)60 Correction Calculator is a free spt correction for geotechnical engineers and foundation designers — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About SPT N60 & (N1)60 Correction Calculator
Correct a field SPT blow count for hammer energy and overburden — the N60 and (N1)60 every correlation needs. The calculation implements N60 = N × ER/60; CN = √(95.76/σ′v) ≤ 1.7 (Liao–Whitman); (N1)60 = CN × N60 (Liao & Whitman (1986); Skempton (1986)). Raw N values from different rigs aren't comparable — an automatic hammer delivers ~30% more energy than a donut hammer on the same sand. Every modern correlation (liquefaction, φ, bearing) expects (N1)60, not field N.
How to use SPT N60 & (N1)60 Correction Calculator
- 1Enter Field N (blows/300 mm).
- 2Enter Hammer energy ratio in % (Safety hammer ~60 · donut ~45 · automatic 80+).
- 3Enter Effective overburden σ′v in kPa.
- 4Read N60, CN (overburden factor), (N1)60 instantly — no submit button needed.
- 5Need US units? Flip the SI/Imperial toggle and every field converts.
Why use SPT N60 & (N1)60 Correction Calculator?
- ✓Implements the standard formula — N60 = N × ER/60; CN = √(95.76/σ′v) ≤ 1.7 (Liao–Whitman); (N1)60 = CN × N60
- ✓Reference cited on-page: Liao & Whitman (1986); Skempton (1986)
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Live worked example: the substitution recomputes from your numbers
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the SPT N60 & (N1)60 Correction Calculator use?+
It computes N60 = N × ER/60; CN = √(95.76/σ′v) ≤ 1.7 (Liao–Whitman); (N1)60 = CN × N60, per Liao & Whitman (1986); Skempton (1986). The formula is displayed under the result along with a worked example substituted with your own inputs.
What should I keep in mind when using this calculator?+
Raw N values from different rigs aren't comparable — an automatic hammer delivers ~30% more energy than a donut hammer on the same sand. Every modern correlation (liquefaction, φ, bearing) expects (N1)60, not field N. Note: Educational aid — site characterization requires a geotechnical engineer.
Can this replace a soil investigation?+
No calculator replaces boreholes and lab tests — but with investigated parameters in hand, this gives you the standard-method result instantly, with the formula shown so reviewers can check it.
Is the SPT N60 & (N1)60 Correction Calculator free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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