Craft Quantities
Plan & Takeoffs

Materials & Quantities

Concrete Slump Flow Test Calculator (ASTM C1611)

Classify a self-consolidating concrete (SCC) mix's flowability and viscosity from a slump flow test reading.

  • Answers as you type
  • Every formula cited
  • Calculated in your browser
SettingsSettings for this calculationUS
Market
Imperial · sales tax
The first of two perpendicular spread diameter measurements.

Measure the concrete patty's diameter in two directions roughly 90° apart after lifting the slump cone.

The second perpendicular spread diameter measurement.

The two measurements should be reasonably close — a large difference between them can itself indicate segregation.

The time in seconds for the concrete to reach the marked spread circle.

Start timing the moment the cone is fully lifted; stop when the spread first touches the circle marked on the base plate — 500 mm in EN 12350-8, 20 in in ASTM C1611.

Average slump flow

26.5 in

High confidence

Flowability class: SF2. Viscosity class: VS2 (more viscous, better segregation resistance).

Diameter spread between the two readings
1 in
T50 spread time
3 s
Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

  • ASTM C1611 slump flow test procedure and EFNARC/ACI SF1-SF2-SF3 flowability classes (SF1: 550-650mm, SF2: 651-750mm, SF3: 751-850mm) and VS1/VS2 viscosity classes based on the T50 spread time (VS1 ≤ 2s, VS2 > 2s)

Inputs used

Spread Diameter 1
27 in
Spread Diameter 2
26 in
T50 Spread Time
3

Intermediate steps

Diameter spread between the two readings
1 in
T50 spread time
3 s
Final result26.5 in

Confidence note: Flowability class: SF2. Viscosity class: VS2 (more viscous, better segregation resistance).

What this calculation does not cover

  • The two readings are averaged whatever the gap between them. ASTM C1611 treats a difference of more than 50mm between the perpendicular diameters as grounds to discard that test and repeat it, so a 700/620mm pair is not a 660mm SF2 mix — it is a test that has not yet produced a usable number, and this page lowers its confidence rather than withholding the average.
  • Flowability is not passing ability. A mix can spread to SF2 or SF3 on an open base plate and still arch and block between closely spaced bars, which is why passing ability is measured separately with a J-Ring (ASTM C1621) or an L-box, comparing an obstructed spread against this free one. Nothing entered here describes bar spacing, cover or maximum aggregate size.
  • T50 describes how the mix behaves while it is still moving, not whether it stays uniform once it stops. Static segregation — coarse aggregate settling through a deep lift, a mortar-rich layer forming at the top — is judged by a column or sieve segregation test and by the visual stability rating of the patty, none of which this page calculates, so an SF2/VS2 pair is not by itself evidence of a stable mix.
  • The viscosity class is a hard cut at exactly 2 seconds, and T50 is hand-timed from the cone clearing the concrete to the spread first touching the 500mm circle. Half a second of operator variation moves a mix from VS1 to VS2, so readings either side of 2s are one borderline band rather than two different mixes.
  • A flow class is a target chosen for a particular element, not a grade to be maximised, and it says nothing about what the mix does to the formwork. SF3 is specified for heavily congested or complex sections rather than being an improvement on SF1, and self-consolidating concrete of any class can act on the form at close to full hydrostatic pressure, which is a separate calculation from anything on this page.

Add the equipment this sizes

This result is a specification — 26.5 in — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

2.25 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1

Regulatory standards & verification citations1
  1. ASTM C1611 slump flow test procedure and EFNARC/ACI SF1-SF2-SF3 flowability classes (SF1: 550-650mm, SF2: 651-750mm, SF3: 751-850mm) and VS1/VS2 viscosity classes based on the T50 spread time (VS1 ≤ 2s, VS2 > 2s)

Which documents these citations point at

Standards referenced: ASTM C1611 (ASTM International, United States).

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Tools and safety for this job

To place and finish concrete, erect formwork and saw-cut cured concrete. Generic types, no brands, no prices.

Protection this work requires

  • Cutting or grinding concrete, masonry, screed, tile or fibre-cement board releases respirable silica: cut wet or extract at the tool, and wear a P2/N95 respirator at minimum — a nuisance dust mask does not filter it.
  • Hardwood dust is a recognised carcinogen: extract at the tool and wear a P2/N95 respirator when cutting or sanding indoors.
  • Wet cement and lime burn skin and eyes painlessly until the damage is done: waterproof gloves to EN 374, safety glasses whenever the mix can splash, and never kneel in wet mix in permeable trousers.
  • Saws, grinders and breakers run above 85 dB, where hearing damage accumulates and does not recover: defenders or plugs for every cut, not just the long ones.
  • Breakers and grinders cause permanent nerve damage: limit continuous trigger time, keep hands warm, and stop if fingers tingle or blanch.
  • Boards, blocks and bagged material cause most lasting back injuries on small sites: two people or a lifter for full sheets, and never a bag on one shoulder up a ladder.
Show the 17 tools this job needs

Essential

  • Angle grinder

  • Bull float and edger

  • Circular saw

  • Claw hammer

  • Dust extractor or vacuum with a fine filter

  • Screed bar or rail

  • Shovel and spade

  • Spirit level

  • String line and pins

  • Tape measure

  • Wheelbarrow

Recommended

  • Chalk line

  • Cordless drill/driver

  • Floor or cut-off saw

  • Plate compactor

  • SDS rotary hammer

Optional

  • Power float

Also needed as materials: chalk refill, circular saw blades, cutting and diamond discs, diamond blades, drill and driver bits, SDS bits and chisels.

what each concrete tool is for, and the spec that decides which to buy where one does.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Called something else where you work? Placing and compaction — the term in each market, how close the equivalence really is, and the standard that governs it.

How to calculate concrete slump flow test (ASTM C1611) in 4 steps

  1. Spread Diameter 1The first of two perpendicular spread diameter measurements.
  2. Spread Diameter 2The second perpendicular spread diameter measurement.
  3. T50 Spread TimeThe time in seconds for the concrete to reach the marked spread circle.
  4. Average slump flowThe tool computes the average slump flow from those figures and shows the formula, its sources, and a confidence rating alongside it.

Average slump flow by spread diameter 1

Page defaults, not your figures above.

Spread Diameter 1Average slump flow (in)
15 in20.7
20 in23.2
25 in25.7
30 in28.2
35 in30.7

Frequently asked questions

What does the slump flow diameter tell me?
It's a direct measure of the mix's flowability under its own weight — larger spread means a more flowable mix, useful for congested reinforcement or complex formwork, but excessive spread can also signal segregation.
Why does T50 (spread time) matter separately from the final diameter?
Two mixes can reach the same final spread diameter at very different speeds — T50 measures viscosity, which affects how the mix behaves while filling formwork and how much time workers have before it locks in place.
What is a Visual Stability Index (VSI)?
A separate 0-3 visual rating (not calculated here) for segregation signs like a mortar halo around the patty's edge or coarse aggregate piling at the center — always inspect the actual test patty, since numbers alone don't catch every segregation sign.
Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.