2026-10-23T19:17:32

Concrete Grade K to fc Conversion: K-300 Is About 25 MPa (Bina Marga Table 6)

Concrete grade K to fc conversion is a common source of confusion: a ready-mix supplier writes K-300 while the structural drawing says fc 25 MPa. Table 6 of the Ministry of Public Works guideline Pd T-07-2005-B pairs K-300 with fc 25 MPa on a 15 x 30 cm cylinder, while the practical rule (divide K by 10, multiply by 0.83 because cube specimens read higher) gives 24.90 MPa. This article shows both figures side by side as of 23 October 2026, the gaps between them, and how to write the concrete grade in a quote to avoid misreading.

Concrete grade K to fc conversion: official Pd T-07-2005-B table and practical rule

Grade K (kg/cm2)	fc per Table 6 (MPa, 15x30 cylinder)	Practical rule K/10 x 0.83 (MPa, homeX calculation)	Minimum strength 7 days / 28 days, Table 6 (MPa)	Source
K-125	10	10.38	7.0 / 10.5	Kementerian PU (Bina Marga)
K-175	15	14.53	9.5 / 14.5	Kementerian PU (Bina Marga)
K-250	20	20.75	15.0 / 21.0	Kementerian PU (Bina Marga)
K-300	25	24.90	18.0 / 25.0	Kementerian PU (Bina Marga)
K-350	30	29.05	21.0 / 29.0	Kementerian PU (Bina Marga)
K-400	35	33.20	24.0 / 33.0	Kementerian PU (Bina Marga)
K-500	45	41.50	26.0 / 40.0	Kementerian PU (Bina Marga)
K-600	50	49.80	32.5 / 50.0	Kementerian PU (Bina Marga)
K-100	Not in Table 6	8.30 (Megacon table: 8.3)	—	Megacon Perkasa
K-150	Not in Table 6	12.45 (Megacon table: 12.35)	—	Megacon Perkasa
K-200	Not in Table 6	16.60 (Megacon table: 16.60)	—	Megacon Perkasa
K-225	Not in Table 6	18.68 (Megacon table: 18.68)	—	Megacon Perkasa
K-275	Not in Table 6	22.83 (Megacon table: 22.83)	—	Megacon Perkasa

Source: Ministry of Public Works (Bina Marga), guideline Pd T-07-2005-B Concrete works for roads and bridges, Table 6 (values printed as is; table note: g = 10 m/s2) and clause 9.2; Megacon Perkasa for the 0.83 factor and the K-100 to K-500 table. The practical-rule column is calculated by homeX; the Megacon table lists K-150 = 12.35 although 150/10 x 0.83 = 12.45, so we show both our calculation and its table value. With the physical conversion 1 MPa = 10.197 kgf/cm2, K-300 becomes about 24.42 MPa (homeX calculation). Data gaps: the guideline is for roads and bridges (2005, citing older SNI); for building structures the grade and test method follow the current structural concrete SNI and the structural engineer drawings, whose text we did not read. The 28-day column in Table 6 does not always equal fc (e.g. K-500: 40.0 vs 45); we have not corrected it.

Why K and fc differ

Per Megacon Perkasa, grade K comes from the 1971 Indonesian Reinforced Concrete Regulation and uses a 15 x 15 x 15 cm cube specimen, while grade fc (MPa) follows SNI 03-2847-2002 and uses a 15 x 30 cm cylinder. Strength ratios of specimens in that source: 15 cm cube = 1.00; 20 cm cube = 0.95; 15 x 30 cylinder = 0.83. The Bina Marga guideline says cube specimens are strongly discouraged, and if still used the result must be converted to cylinder.

Acceptance criteria in the guideline

Clause 9.2 requires a test set of at least four pairs of 150 x 300 mm cylinders tested at 3, 7, 14 and 28 days. Strength is considered satisfactory when the average of at least four consecutive results is not less than fc + S (S = standard deviation) and no single result is below 0.85 fc. homeX calculation: for K-300 (fc 25 MPa) the 0.85 fc limit is 21.25 MPa. This guideline is for roads and bridges; for buildings ask for the criteria in the project drawings and specification.

How to write the concrete grade in a quote

homeX analysis, not a standard quote: write both, for example "fc 25 MPa (equivalent K-300), 15 x 30 cm cylinder test at 28 days, slump per specification", and ask the supplier to state whether their K grade is cube-based. Price per m3 for K-225 to K-300 is in the homeX ready-mix price article; slab pouring cost is in a separate article.

Buyer tips

Write fc in MPa and K side by side in contracts and purchase orders.
Ask for cylinder test results or their conversion, not only cube figures.
Do not assume K-225 = fc 22.5; the practical calculation is about 18.68 MPa.
For important structures, ask the structural engineer which conversion applies.

Request a concrete grade K to fc conversion quote for your project

homeX can compare several brands at once and prepare a written quote for projects, renovations or shop stock. Send your needs (brand, size, quantity, location) via WhatsApp +62 821 1818 998, or visit the homeX showroom: Priskilla Tower, 6th floor, Jl. Atang Sanjaya No.21, Benda, Kota Tangerang, Banten 15125. Visit the homeX Showroom.

Disclaimer: prices change without notice and differ by store, city, pack size, grade and promotion. Data as of 23 October 2026; always confirm with the seller before buying.

FAQ

K-300 equals what fc in MPa? Table 6 of Pd T-07-2005-B pairs K-300 with fc 25 MPa (15 x 30 cylinder). The practical rule K/10 x 0.83 gives 24.90 MPa; the physical conversion 1 MPa = 10.197 kgf/cm2 gives about 24.42 MPa (homeX calculation).

Why does K-500 differ so much between table and rule? Table 6 pairs K-500 with fc 45 MPa while the practical rule gives 41.50 MPa. We found no explanation of this gap in the guideline; use the value stated in the project specification.

Does this article include concrete prices? No. Ready-mix prices per m3 are covered in the homeX ready-mix price article; this one is only about grade terms, conversion and test acceptance.