Hip / Valley Rafter Length Calculator

Diagonal-run math for regular hips and valleys — not the common-rafter calculator

Starting point only — not gospel. This is layout math for a regular (equal-pitch) hip or valley on a 90° corner: diagonal run = common run × 1.4142, then length = √(diagonal run² + rise²). IRC Chapter 8 roof framing (R802) still governs member size, species, spans, connections, and bracing. Hip and valley framing is more than this length: ridge intersections, backing (cheek) bevels, and a skewed birdsmouth often need a framing square or rafter table cross-check on the real stock. Not a substitute for the adopted code or a stamped drawing.

Embed this calculator Free · no API key · keep the attribution link

Copy the snippet below to embed this calculator on your site. The attribution link must stay intact and dofollow (no rel="nofollow"). Browse all embeddable calculators

Theme Width

<div class="ttq-embed" style="max-width:100%;margin:0 auto;">
  <iframe src="https://testtalkhq.com/embed/hip-valley-rafter-length-calculator/?theme=light&utm_source=embed" width="100%" height="980" frameborder="0" loading="lazy" scrolling="no" title="Hip / Valley Rafter Length Calculator — TestTalkHQ" style="border:0;max-width:100%;width:100%;"></iframe>
  <p style="font:400 13px/1.4 system-ui,sans-serif;text-align:center;margin:6px 0 0;">Powered by the <a href="https://testtalkhq.com/hip-valley-rafter-length-calculator/?utm_source=embed&utm_medium=referral&utm_campaign=calculator_embed&utm_content=hip-valley-rafter-length-calculator" target="_blank" rel="noopener">Free Hip / Valley Rafter Length</a> from <a href="https://testtalkhq.com/?utm_source=embed&utm_medium=referral&utm_campaign=calculator_embed&utm_content=hip-valley-rafter-length-calculator" target="_blank" rel="noopener">TestTalkHQ</a></p>
</div>

<div class="ttq-embed" style="max-width:100%;margin:0 auto;">
  <iframe src="https://testtalkhq.com/embed/hip-valley-rafter-length-calculator/?theme=light&utm_source=embed" width="100%" height="980" frameborder="0" loading="lazy" scrolling="no" title="Hip / Valley Rafter Length Calculator — TestTalkHQ" style="border:0;max-width:100%;width:100%;"></iframe>
  <p style="font:400 13px/1.4 system-ui,sans-serif;text-align:center;margin:6px 0 0;">Powered by the <a href="https://testtalkhq.com/hip-valley-rafter-length-calculator/?utm_source=embed&utm_medium=referral&utm_campaign=calculator_embed&utm_content=hip-valley-rafter-length-calculator" target="_blank" rel="noopener">Free Hip / Valley Rafter Length</a> from <a href="https://testtalkhq.com/?utm_source=embed&utm_medium=referral&utm_campaign=calculator_embed&utm_content=hip-valley-rafter-length-calculator" target="_blank" rel="noopener">TestTalkHQ</a></p>
</div>
<script>(function(){function r(e){if(!e||!e.data||e.data.type!=="ttq-embed-height")return;var h=+e.data.height;if(!h)return;document.querySelectorAll("iframe[src*='testtalkhq.com/embed/']").forEach(function(f){if(!e.source||f.contentWindow===e.source)f.style.height=h+"px"})}window.addEventListener("message",r)})();</script>

Any trade

Contractor Job Estimator

Price remodels and GC work, then send a quote with no internal numbers.

Excel or Google Sheets. Best on a computer.

$29.00

Buy

See all products

Checkout opens in a new tab.

Hip / Valley Layout Gear

A framing square still walks the hip — unit rise and the 17-inch hip run on the body, not 12. Confirm the calculator plumb before the first kerf.

Swanson Speed Square

Pivot to the hip plumb from the results, not the common 6/12 mark. Confirm against the calculator degree before the ridge cut.

View on Amazon →

16×24 Framing Square

Hip layout is 17 on the body (12 × 1.4142) and the pitch number on the tongue. Stair gauges lock both so the walk does not drift.

View on Amazon →

Johnson Stair Gauges

Clamp 17 and the pitch. Same hardware as a stringer or common walk — different numbers for a hip.

View on Amazon →

7-1/4" Circular Saw

Set bevel to hip plumb for the ridge. Backing cuts and the skewed birdsmouth are separate kerfs — do not overcut remaining depth.

View on Amazon →

48" Box Beam Level

Prove plates and the ridge before the first hip. A hip that is “long” is often a ridge that is off layout, not bad math.

View on Amazon →

Why × 1.4142

How diagonal run, hip plumb, and seat cut come off the common triangle. Use the calculator, then this guide on the stock.

Read the Layout Guide →

As an Amazon Associate, TestTalkHQ earns from qualifying purchases.

How to Use This Hip / Valley Rafter Calculator

Type the same common run you would give the common rafter calculator — plate to ridge, horizontal, feet and inches. Then the roof pitch as 6/12 or in degrees. Optional: rafter/ridge thickness for the ridge plumb setback, and level overhang for the tail. Read hip/valley length, the diagonal run actually used, hip plumb, and seat cut.

diagonal run = common run × 1.4142
length = √(diagonal run² + rise²) = diagonal run ÷ cos(hip pitch)

The 1.4142 is √2 for a 90° corner: the hip walks the diagonal of the common-run square. Rise does not get that factor. That is why you must not multiply common rafter length by 1.4142. Walkthrough: diagonal-run method guide. If the pair misses the ridge: troubleshooting. Decision (common vs this math): common vs hip/valley.

Hip / Valley Rafter Length Calculator